Role of PET/CT in Carcinoma of the Pancreas

Introduction

Pancreatic Malignancies

Pancreatic cancer is the 12th most common cancer globally but the 7th leading cause of cancer-related mortality, accounting for 4–5% of all cancer-related deaths worldwide. Most tumours are of exocrine origin, with pancreatic ductal adenocarcinoma (PDAC) dominating both incidence and clinical burden.

Pancreatic Ductal Adenocarcinoma

• Most prevalent histologic subtype of pancreatic cancer (85–90% of cases)
• Peak incidence in the sixth to seventh decades of life
• Slight male predominance

Risk Factors

• Cigarette smoking (major modifiable risk factor)
• Diabetes mellitus
• Family history of pancreatic cancer in first-degree relatives
• Associated genetic syndromes:
• BRCA2 mutation
• Hereditary pancreatitis (PRSS1)
• Lynch syndrome (MLH1, MSH2)
• Familial atypical multiple mole melanoma (FAMMM; CDKN2A)
• Peutz–Jeghers syndrome (STK11)
• Ataxia-telangiectasia (ATM)

Molecular Pathogenesis

PDAC develops through a stepwise accumulation of genetic alterations. The most common precursor lesions include pancreatic intraepithelial neoplasia (PanIN), intraductal papillary mucinous neoplasm (IPMN), and mucinous cystic neoplasm (MCN).

Common driver mutations

These molecular alterations contribute to uncontrolled proliferation, resistance to apoptosis, invasion, and metastasis.

Anatomy and Pathology

Anatomy

• The pancreas is a retroperitoneal organ measuring 12–15 cm in length and lacks a true capsule, facilitating early local tumour invasion.
• It is anatomically divided into five components: head, uncinate process, neck, body, and tail.
• Arterial supply is derived from the gastroduodenal artery (via the superior pancreaticoduodenal branches), the inferior pancreaticoduodenal artery (from the superior mesenteric artery), and branches of the dorsal pancreatic and splenic arteries.
• Venous drainage occurs through tributaries to the superior mesenteric vein (SMV) and splenic vein, which unite posterior to the pancreatic neck to form the portal vein.
• Major nodal stations include peripancreatic, celiac, common hepatic artery, superior mesenteric, and para-aortic nodes. These represent the first echelon of metastatic spread.
• The pancreas is surrounded by rich autonomic neural plexuses. Perineural invasion is extremely common in PDAC and contributes to severe back pain, local recurrence, and poor prognosis.

Histology

• The exocrine component (≈85–90%) consists of acinar and ductal cells responsible for digestive enzyme and bicarbonate secretion.
• The endocrine component (islets of Langerhans) includes:
• Alpha cells — glucagon
• Beta cells — insulin
• Delta cells — somatostatin
• PP cells — pancreatic polypeptide

Histopathology

Pancreatic Ductal Adenocarcinoma

• PDAC is the most common solid malignant neoplasm of the pancreas, accounting for approximately 85–90% of all pancreatic malignancies.
• PDAC originates from ductal epithelial cells and is characterised by irregular infiltrating glands, dense desmoplastic stroma, perineural invasion, lymphovascular invasion, and early metastatic potential.
• The pancreatic head is the most frequently involved site (60–70%), followed by the body (15–20%) and tail (10–15%).

Histological Variants

Desmoplastic Reaction

A hallmark of PDAC is an abundant fibrotic stroma composed of cancer-associated fibroblasts, collagen, immune cells, and extracellular matrix. This dense stromal environment contributes to poor drug delivery, hypoxia, and treatment resistance. It also provides the biological rationale for FAP-targeted PET imaging, discussed later in this chapter.

Clinical Presentation and Tumour Markers

Clinical Presentation

• Typically asymptomatic in early stages; most patients present late with advanced disease.
• Common symptoms include painless jaundice (head tumours), epigastric or left-sided pain (body/tail tumours), weight loss, fatigue, new-onset diabetes, and steatorrhoea. Symptoms are non-specific, leading to delayed diagnosis.
• Laboratory findings often show cholestatic LFT derangement and mild hyperglycaemia.

Tumour Markers

Tumour markers are adjunctive biomarkers that assist in the diagnosis, prognostication, treatment monitoring, and surveillance of pancreatic cancer. They should never be used as standalone diagnostic tests, as benign hepatobiliary diseases and other gastrointestinal malignancies can produce similar elevations.

CA 19-9 (Carbohydrate Antigen 19-9)

CA 19-9 remains the most widely used serum biomarker in PDAC. It is a sialylated Lewis blood-group antigen expressed by pancreatic ductal epithelial cells. Approximately 75–85% of patients with PDAC demonstrate elevated serum CA 19-9 levels. However, around 5–10% of the population are Lewis antigen-negative (Le a−b−) and therefore cannot synthesise CA 19-9, even in advanced disease. Consequently, a normal CA 19-9 level does not exclude malignancy.

Clinical Applications

✓ Supports diagnosis in patients with suspicious imaging

✓ Baseline prognostic marker

✓ Predicting resectability

✓ Monitoring chemotherapy response

✓ Detecting recurrence

Limitations

CA 19-9 may be elevated in acute, chronic, and autoimmune pancreatitis; cholangitis; choledocholithiasis; benign biliary obstruction; hepatocellular dysfunction; and gastric, colorectal, and cholangiocarcinoma. Therefore, elevated CA 19-9 + obstructive jaundice ≠ pancreatic cancer — always interpret alongside imaging.

Other Tumour Markers

• CEA (carcinoembryonic antigen) — elevated in approximately 30–60% of cases; less sensitive and less specific than CA 19-9.
• CA 50 — elevated in roughly 50–70% of pancreatic cancers; limited additional value over CA 19-9.
• CAM 17-1 (cell adhesion molecule 17-1) — reported elevation in ~40–60% of cases; mainly of adjunctive or investigational value.

Staging of Pancreatic Ductal Adenocarcinoma

AJCC 8th edition TNM classification. The current standard classifies disease according to primary tumour size / arterial involvement (T), nodal burden (N), and distant metastasis (M).

Primary Tumour (T)

T classification is primarily size-based, except for T4, which reflects major arterial invasion.

Regional Lymph Nodes (N)

Distant Metastasis (M)

Stage Grouping

Patterns of Tumour Spread

Tumour dissemination in pancreatic cancer is primarily dictated by anatomic location and proximity to major vascular and neural structures.

Local Extension

PDAC spreads early because the pancreas lacks a true capsule, has abundant lymphatics and extensive neural plexuses, and lies adjacent to major vessels. Tumour commonly invades the superior mesenteric artery (SMA), superior mesenteric vein (SMV), portal vein, celiac axis, and common hepatic artery.

• Head and uncinate tumours commonly involve the SMA, SMV, portal vein, and common hepatic artery (CHA).
• Body tumours tend to infiltrate the celiac axis and splenic vessels.
• Tail tumours extend along the splenic artery and vein and may directly invade adjacent organs such as the stomach, splenic flexure of the colon, spleen, and left adrenal gland.

Nodal Dissemination

• Regional peripancreatic lymph nodes are the first echelon of spread; nodal metastases are present in approximately 60–70% of patients at diagnosis (and in up to 80–85% of advanced tumours).
• Pancreatic head tumours most commonly involve peripancreatic nodes (≈60–70%), followed by hepatic artery / portal (≈30–50%) and celiac nodes (≈20–30%).
• Body and tail tumours frequently spread to splenic hilar nodes (≈40–60%) and left gastric nodes (≈20–40%).
• Advanced disease may involve retroperitoneal and para-aortic nodal stations (≈15–25%), which carries a poor prognosis.

Distant Metastasis

• Liver — most common site; present in approximately 50–70% of patients with metastatic disease at diagnosis.
• Peritoneum — seen in about 25–40% of advanced cases.
• Lung — approximately 10–20% of patients, often later in the disease course.
• Bone (osseous) — relatively uncommon, reported in 5–10% of cases, typically in late-stage disease.

Imaging of Pancreatic Cancer

Imaging Work-up of Suspected Pancreatic Cancer

1.Transabdominal Ultrasound (USG)

Transabdominal ultrasound is often the initial investigation in patients presenting with abdominal pain and obstructive jaundice. It has limited sensitivity for detecting the primary pancreatic mass but is useful for evaluating gallstones, gallbladder wall thickening, and pericholecystic fluid, and for identifying the level of biliary obstruction.

2. Endoscopic Retrograde Cholangiopancreatography (ERCP)

ERCP is commonly performed after ultrasound demonstrates common bile duct obstruction, serving both diagnostic and therapeutic roles. Malignant strictures typically show irregular narrowing with an abrupt ductal cut-off, whereas benign strictures are usually smooth and tapering, although overlap exists. Cytologic brushings obtained from the stricture site can facilitate histopathologic diagnosis, and ERCP also enables biliary stent placement for decompression.

3. Computed Tomography

Pancreatic-Protocol CT

Multiphasic contrast-enhanced CT remains the cornerstone of pancreatic cancer evaluation, accurately assessing the primary tumour, vascular invasion, liver metastases, regional nodes, and surgical resectability.

Recommended Protocol

• Non-contrast (optional)
• Rapid contrast injection at 4–5 mL/sec over approximately 30 seconds.
• Pancreatic parenchymal phase (35–45 sec)
• Portal venous phase (65–70 sec): optimal for liver metastasis.
• Thin slices (≤ 1 mm)
• Multiplanar reconstructions

CT Appearance of PDAC

Pancreatic adenocarcinoma typically appears as an ill-defined, mildly hypodense solid mass relative to normal pancreatic parenchyma. Approximately 60% arise in the head, 15% in the body, and 5% in the tail, with up to 20% presenting as diffuse glandular involvement. Secondary features include upstream pancreatic atrophy, focal gland enlargement, abrupt cut-off of the pancreatic and/or common bile duct (double-duct sign), and evidence of extrapancreatic extension.

The overall sensitivity of CT for detecting the primary tumour ranges from 86% to 97%, but declines to around 77% for tumours smaller than 2 cm.

Assessing Resectability

Vessel abutment — ≤ 180° contact — is potentially resectable or borderline.

Vessel encasement — > 180° contact — usually indicates unresectable arterial disease.

Lymph Nodes on CT

• Assessment relies primarily on size criteria, with a short-axis diameter > 1 cm considered suspicious, though non-specific.
• Raising the threshold to > 1.5 cm markedly reduces sensitivity (~16.7%).
• Additional suspicious features include rounded morphology, hypodensity, and ill-defined margins.
• Major limitations include the inability to detect micrometastases and difficulty distinguishing malignant from reactive nodes.

4. MRI

MRI is particularly valuable when CT is indeterminate, when a contrast allergy exists, and for characterising liver lesions and cystic pancreatic lesions. Advantages include superior soft-tissue contrast, excellent liver imaging, and MRCP assessment.

5. Endoscopic Ultrasound (EUS) with FNA

EUS enables real-time imaging and tissue sampling without intravenous contrast and is highly sensitive for detecting small pancreatic tumours, with reported sensitivity up to 90% and specificity around 94%. For vascular assessment it is less accurate than CT, and the "loss of echoplane" sign is unreliable, as true vascular invasion is uncommon even when the sign is present.

EUS (± FNA) identifies malignant lymph nodes by features such as hypoechoic texture, rounded morphology, and absence of an echogenic hilum, and EUS-guided fine-needle aspiration enhances diagnostic accuracy through cytologic confirmation. However, its limited field of view may fail to detect distant nodal stations, including para-aortic and mesenteric nodes.

Comparative Summary of Imaging Modalities

Clinical Pearls

• CA 19-9 is a monitoring marker — not a screening test.
• Lewis antigen-negative patients cannot produce CA 19-9.
• CT remains the gold standard for assessing resectability.
• EUS provides the highest diagnostic yield for tissue confirmation.
• PET/CT complements CT by detecting occult metastatic disease rather than evaluating vascular invasion.

Treatment of Pancreatic Cancer

1. Resectable Disease

Surgical resection remains the only potentially curative treatment. Pancreaticoduodenectomy (Whipple procedure) is performed for head lesions, while distal pancreatectomy is used for body and tail tumours. The objective is an R0 resection (negative margins). Adjuvant chemotherapy significantly improves survival, with modified FOLFIRINOX preferred for fit patients and gemcitabine-based regimens reserved for selected or less-fit individuals.

2. Borderline Resectable Disease

Neoadjuvant therapy (chemotherapy ± chemoradiation) is recommended to downstage the tumour and improve the likelihood of an R0 resection. Following treatment, patients are restaged, and surgery is considered if there is no disease progression.

3. Locally Advanced (Unresectable) Disease

Upfront surgery is not indicated. Management consists primarily of systemic chemotherapy (FOLFIRINOX or gemcitabine-based regimens). Chemoradiation may be considered in selected cases for local control. Patients should be periodically reassessed for potential conversion to resectable status.

4. Metastatic Disease

Systemic chemotherapy is the mainstay. FOLFIRINOX is preferred in patients with good performance status, while gemcitabine plus nab-paclitaxel is an alternative. Palliative radiotherapy may be used for symptom control, and comprehensive supportive care is essential.

5. Palliative Interventions

Endoscopic biliary stenting (via ERCP) relieves obstructive jaundice. Surgical or endoscopic bypass may be considered in selected patients. Effective pain management — including analgesics and celiac plexus block — is crucial for quality of life.

PET/CT in Pancreatic Cancer

Pancreatic ductal adenocarcinoma (PDAC) is characterised by aggressive tumour biology, early metastatic spread, and a dense desmoplastic stromal reaction. While contrast-enhanced CT provides excellent anatomical detail, it cannot directly evaluate tumour metabolism. ¹⁸F-FDG PET/CT complements conventional imaging by demonstrating glucose metabolism, allowing earlier detection of viable tumour, occult metastases, and treatment response before structural changes become apparent.

Unlike CT, PET answers a biological question — “Is this tissue metabolically active?” — rather than simply “Does this tissue appear abnormal?” This distinction explains why PET/CT is particularly valuable in staging, response assessment, and recurrence detection.

Biological Basis of FDG Uptake

Cancer cells exhibit increased glycolysis despite adequate oxygen availability — a phenomenon known as the Warburg effect. This metabolic reprogramming results in increased glucose-transporter (GLUT-1, GLUT-3) expression, increased hexokinase activity, reduced glucose-6-phosphatase activity, and enhanced intracellular trapping of FDG. Consequently, most PDACs demonstrate intense FDG uptake.

Tracers

Several radiotracers are available for pancreatic imaging, targeting different biological processes — glucose metabolism, stromal activation, somatostatin-receptor expression, and integrin-mediated adhesion. ¹⁸F-FDG remains the workhorse, while ⁶⁸Ga-labelled agents are expanding the field.

Which Tracer Should Be Used?

✓ Pancreatic ductal adenocarcinoma → FDG PET/CT

✓ Neuroendocrine tumour → DOTATATE PET/CT

✓ Emerging research → FAPI PET/CT

Patient Preparation

Proper preparation is essential because physiological glucose metabolism directly influences image quality.

Recommended Preparation

• Fast for 4–6 hours
• Hydration encouraged
• Blood glucose preferably < 150 mg/dL (acceptable < 200 mg/dL depending on protocol)
• Avoid strenuous exercise for 24 hours
• Keep patient warm to reduce brown-fat uptake
• Rest quietly after injection

Why Hyperglycaemia Matters

Pancreatic cancers tend to show hyperglycemia. High serum glucose competes with FDG for GLUT transporters, resulting in reduced tumour uptake, false-negative scans, and underestimation of SUV.

PET Acquisition Protocol

• Whole-body acquisition from skull base to mid-thigh
• FDG dose according to body weight
• Uptake period: approximately 60 minutes
• Low-dose CT for attenuation correction
• Diagnostic contrast-enhanced CT when indicated

Image Interpretation

PET interpretation should never rely on SUV alone. Every lesion should be evaluated using three complementary parameters:

1 · Pattern

Focal · diffuse · multifocal.

2 · Intensity

Measured using SUVmax, SUVmean, and SUVpeak.

3 · CT Morphology

Assess enhancement, margins, duct dilatation, calcification, cystic change, and vascular invasion.

Role of PET/CT in Diagnosis

Is PET recommended for initial diagnosis? No. Major international guidelines consistently recommend pancreatic-protocol contrast-enhanced CT as the first-line imaging investigation. PET/CT serves as an adjunctive problem-solving tool rather than a replacement for CT.

When PET Adds Value

• CT findings are equivocal
• Differentiating viable tumour from fibrosis
• Suspected occult metastases
• Discordance between imaging and CA 19-9
• Indeterminate recurrent disease
• Preoperative staging in selected patients

PET Appearance of PDAC

Typical findings include intense focal FDG uptake corresponding to a hypoenhancing pancreatic mass, irregular margins, the double-duct sign, peripancreatic fat infiltration, regional nodal uptake, and liver metastases. SUV values vary widely; although many tumours demonstrate SUVmax > 5, SUV thresholds should never be used as the sole diagnostic criterion because inflammatory lesions may show similar uptake.

Inflammatory conditions that frequently show increased FDG uptake include autoimmune pancreatitis, acute and chronic pancreatitis, pancreatic abscess, and post-procedural inflammation.

Differential diagnosis

Autoimmune Pancreatitis vs PDAC

PET in Cystic Pancreatic Lesions

Most pancreatic cysts are benign. However, FDG uptake within mural nodules or enhancing solid components raises concern for invasive carcinoma or high-grade dysplasia. PET should always be interpreted alongside MRI, EUS, CA 19-9, and clinical history.

Peripancreatic fat stranding (increased fat attenuation on CT) may reflect either inflammation or desmoplastic reaction / early extrapancreatic extension; any associated FDG uptake is non-specific and must be correlated with the primary lesion and overall findings.

False Negatives

• Hyperglycaemia (a common feature of pancreatic disease)
• Mucinous tumours
• Necrotic tumours
• Liver and peritoneal metastases < 1 cm
• Small tumors : sensitivity declines to nearly 43% in sub-centimetre lesions owing to spatial-resolution limits and low metabolic tumour volume.

False Positives

• Acute flare of chronic or autoimmune pancreatitis
• Mass-forming pancreatitis
• Recent radiation therapy
• Recent surgical incision or biopsy, especially around the CBD
• Benign pancreatic pathologies
• Technical factors — misregistration of adjacent bowel uptake, partial-volume averaging

Role of PET/CT in Staging

Once PDAC has been diagnosed, accurate staging becomes the primary objective. The AJCC system incorporates primary tumour extent (T), regional lymph-node involvement (N), and distant metastases (M). The greatest contribution of PET/CT is in evaluating metastatic (M) disease.

Contribution of PET/CT to TNM Staging

T Stage — Primary Tumour

Assessment of tumour size and local extension depends on the tumour–vessel interface, adjacent organ invasion, and the relationship to the SMA, celiac axis, portal vein, and SMV. These anatomical details are best demonstrated with contrast-enhanced CT.

PET/CT provides limited additional information for T staging because of its lower spatial resolution, so small extrapancreatic extension and vascular invasion cannot be reliably assessed. Current evidence consistently indicates that PET/CT should not be used for local tumour staging.

N Stage — Regional Lymph Nodes

Regional lymph-node metastases are common in PDAC. Small nodes may contain metastases, while large nodes may simply be reactive. CT relies mainly on nodal size, whereas PET evaluates metabolic activity. Metastatic nodes usually demonstrate focal FDG uptake, rounded morphology, and corresponding nodal enlargement on CT; common stations include peripancreatic, hepatic-artery, celiac, para-aortic, superior mesenteric, and retroperitoneal nodes.

PET improves specificity compared with CT because metabolically active nodes are more suspicious than enlarged nodes alone. However, sensitivity remains limited (approximately 50–70%) because micrometastases may not accumulate sufficient FDG, small deposits fall below PET resolution, and reactive inflammatory nodes may also be FDG-avid.

M Stage — Distant Metastases

The most important contribution of PET/CT is whole-body detection of distant metastatic disease — where PET most significantly influences patient management. Common metastatic sites include liver, peritoneum, bone, lung, and distant lymph nodes. PET/CT identifies occult metastatic disease in patients who appear potentially resectable on CT, altering management in approximately 10–20% of patients by detecting metastases not seen on contrast-enhanced CT.

Hepatic Metastases

The liver is the commonest site of distant spread. Sensitivity for hepatic metastases is approximately 46% without intravenous contrast, improving to nearly 82% when PET is combined with contrast-enhanced imaging. FDG PET/CT can detect lesions before structural morphological change occurs, though detection remains limited in small-volume deposits and low-FDG-avid lesions.

Peritoneal and Omental Metastases

Peritoneal dissemination is common in advanced PDAC and usually indicates unresectable disease. Typical findings are focal omental uptake, omental caking, mesenteric nodules, and peritoneal implants. Overall sensitivity remains approximately 40 -70%. Small implants (< 5 mm), diffuse infiltrative disease, and low-cellularity lesions may remain PET-negative — a negative PET does not exclude microscopic peritoneal metastases.

Extrahepatic and Whole-Body Disease

A unique strength of PET/CT is whole-body evaluation in a single examination, revealing unexpected disease that a dedicated pancreatic CT would not routinely include:

• Supraclavicular lymph nodes
• Mediastinal nodes
• Skeletal metastases
• Pulmonary nodules
• Soft-tissue metastases

PET/CT and Surgical Resectability

Perhaps the most misunderstood role of PET/CT concerns surgical planning. PET/CT does not determine whether a pancreatic tumour is technically resectable. Technical resectability depends almost entirely on anatomical relationships that require high-resolution contrast-enhanced CT:

• Arterial encasement
• Venous involvement
• Tumour relationship to the SMA
• Tumour relationship to the celiac axis
• Portal vein and SMV involvement

Instead, PET/CT determines whether surgery is clinically appropriate by identifying distant metastatic disease that would render resection futile.

How PET Changes Management

Several studies have demonstrated that PET/CT detects previously unsuspected metastatic disease in approximately 10–20% of patients who appear potentially resectable on CT. As a result, unnecessary laparotomy is avoided, futile Whipple procedures are prevented, systemic therapy begins earlier, treatment costs decrease, and patient morbidity is reduced

Clinical Scenario

PET/CT Versus Conventional Imaging

Decision Algorithm

PET/CT in response assessment

Why Is PET/CT Important After Treatment?

Following surgery, chemotherapy, radiotherapy, or neoadjuvant treatment, clinicians need to answer several critical questions: Has the patient responded to therapy? Is viable tumour still present? Is surgery now feasible? Has the disease recurred? What is the patient’s prognosis?

Conventional imaging evaluates changes in tumour size, whereas PET/CT evaluates changes in tumour metabolism. Because metabolic alterations often precede anatomical changes, PET/CT can detect therapeutic response weeks before significant tumour shrinkage becomes evident.

Role of PET/CT After Neoadjuvant Therapy

Patients with borderline resectable or locally advanced PDAC frequently receive neoadjuvant chemotherapy or chemoradiotherapy before surgery. Afterward, residual fibrosis, inflammation, and oedema may make it difficult for CT to distinguish viable tumour from post-treatment changes. PET/CT helps overcome this limitation by assessing the metabolic activity of the residual lesion.

Goals of PET Response Assessment

• Evaluate treatment efficacy
• Identify non-responders early
• Assess eligibility for surgery
• Predict pathological response
• Estimate long-term prognosis

Categories of Metabolic Response

PET/CT and Surgical Conversion

One of the most important applications of PET/CT is identifying patients whose disease has become surgically resectable after neoadjuvant therapy. Features favouring surgery include a marked reduction in FDG uptake, no new metastatic lesions, stable or improved vascular anatomy on CT, and declining CA 19-9 levels.

Clinical Scenario

PET/CT in Restaging

Restaging is performed after completion of therapy to determine current disease status. PET/CT evaluates the residual primary tumour, nodal disease, distant metastases, treatment response, and new metastatic deposits. Restaging guides decisions regarding surgery, additional chemotherapy, radiotherapy, clinical-trial enrolment, and palliative care.

PET/CT in Recurrence Detection

Following pancreatic surgery, the operative bed frequently contains fibrosis, granulation tissue, surgical clips, and post-radiotherapy changes, which may mimic recurrent tumour on CT. PET/CT identifies metabolically active recurrence, improving diagnostic confidence.

Clinical Situations Where PET Is Helpful

• CA 19-9 is rising
• CT findings are equivocal
• MRI is inconclusive
• Clinical suspicion persists despite negative imaging
• Biopsy is difficult or unsafe

Common Sites of Recurrence

Surgical bed, regional lymph nodes, liver, peritoneum, lung, and bone. Typical PET findings include focal uptake at the operative bed, FDG-avid lymph nodes, new hepatic lesions, peritoneal implants, and pulmonary nodules with increased uptake.

PET Versus CT for Recurrence

CT alone has a sensitivity of approximately 70% and specificity of 80% for recurrence, whereas PET/CT improves performance to a sensitivity of around 88% and specificity of about 89%; combined with contrast-enhanced CT, sensitivity may approach 95%.

Prognostic Role of PET/CT

PET provides prognostic information beyond anatomical staging. Patients with highly metabolically active tumours generally have more aggressive biology, higher metastatic potential, shorter survival, and earlier recurrence.

Quantitative PET Biomarkers

SUVmax

The most commonly reported parameter, representing the highest FDG uptake within a tumour. Higher SUVmax often correlates with poor differentiation, higher tumour grade, and increased aggressiveness, but it reflects only a single voxel and does not represent the entire tumour burden.

SUVmean

The average FDG uptake throughout the lesion — useful for research and volumetric analyses but less commonly reported in routine practice.

SUVpeak

The average uptake within a small region of highest activity. It is less affected by image noise, more reproducible, and preferred in quantitative response assessment.

Metabolic Tumour Volume (MTV)

The volume of metabolically active tumour. Unlike SUVmax, MTV incorporates tumour size and metabolic extent; higher MTV is associated with advanced disease, higher recurrence rates, and reduced survival.

Total Lesion Glycolysis (TLG)

TLG combines metabolic intensity and tumour volume (TLG = SUVmean × MTV), reflecting the total glycolytic burden of the tumour, and has emerged as one of the strongest PET-derived prognostic biomarkers.

Combining PET with CA 19-9

Combining metabolic imaging with serum biomarkers improves risk stratification. Patients with high SUV, high MTV, high TLG, and persistently elevated CA 19-9 typically experience earlier recurrence, lower resectability rates, and shorter survival.

Guideline Recommendations

Major international guidelines consistently affirm that pancreatic-protocol contrast-enhanced CT remains the primary modality for diagnosis and staging of PDAC. ¹⁸F-FDG PET/CT is not recommended as a routine first-line investigation in all newly diagnosed patients and does not replace high-quality multiphasic CT.

NCCN

• Pancreatic-protocol CT is the primary staging investigation.
• PET/CT may be considered in selected patients at high risk for metastatic disease or when occult metastases are suspected.
• PET/CT should not replace contrast-enhanced CT for determining resectability.

ESMO

• PET/CT is not recommended for routine staging, having not shown clear superiority over contrast CT for detecting distant metastases.
• It may yield false positives in inflammatory conditions such as autoimmune or chronic pancreatitis.
• Its principal benefit lies in detecting unsuspected distant metastatic disease and may influence management in selected patients considered for curative surgery.

NICE (UK)

• Recommends FDG-PET/CT staging in patients who appear to have localised pancreatic cancer on CT prior to curative-intent treatment (surgery, radiotherapy, or systemic therapy), to detect occult metastatic disease and avoid non-beneficial intervention.
• Also supports PET/CT when the diagnosis remains uncertain after initial imaging, alongside EUS-guided sampling.

Emerging Tracers

FAPI PET/CT in PDAC

In PDAC, the tumour microenvironment is characterised by dense desmoplastic stroma rich in cancer-associated fibroblasts that overexpress fibroblast activation protein (FAP). FAPI PET/CT targets this stromal component rather than tumour glycolysis, providing a biologically distinct approach to FDG.

Diagnostic Performance

• Higher tumour-to-background ratios than FDG
• Minimal physiologic abdominal uptake
• Improved lesion conspicuity in the pancreas and peritoneum
• Superior detection of primary tumours, peritoneal and omental metastases, and small hepatic metastases

These advantages are particularly relevant in low-FDG-avid tumours (e.g. mucinous variants) and when bowel or hepatic background activity limits FDG interpretation. As a ⁶⁸Ga-labelled tracer, FAPI does not require fasting or specific patient preparation, unlike FDG.

Limitations and Current Position

• Limited large prospective validation
• Uptake in benign fibrosis, inflammation, and postoperative healing
• No current guideline endorsement; not standard of care

FAPI PET/CT is a promising next-generation modality, particularly for peritoneal disease detection and improved lesion contrast, but remains investigational — currently an adjunct research tool rather than a replacement for FDG PET/CT or contrast-enhanced CT.

Trivehexin PET/CT

Trivehexin is an integrin-targeted PET tracer directed at integrins involved in tumour angiogenesis and cell adhesion (commonly αvβ6). In PDAC, integrin overexpression contributes to tumour invasion and metastatic potential.

Potential Clinical Role

• Improved tumour-to-background contrast compared with FDG
• Better delineation of primary tumour extent
• Detection of small metastatic deposits, including peritoneal disease
• Biologic characterisation beyond glycolysis; because integrin expression correlates with aggressiveness, uptake may carry prognostic implications

Like other ⁶⁸Ga-based tracers, Trivehexin PET/CT does not require special preparation or fasting. It currently rests on early-phase clinical data, has no major guideline endorsement, and remains investigational in pancreatic cancer.

Future Directions

Radiomics

Radiomics extracts hundreds of quantitative imaging features from PET/CT beyond visual interpretation, with potential applications in predicting treatment response, estimating survival, molecular subtyping, and risk stratification.

Artificial Intelligence

AI algorithms are increasingly being developed to automatically segment pancreatic tumours, detect subtle metastatic disease, predict recurrence, estimate survival, and integrate PET, CT, MRI, pathology, and genomics into unified predictive models.

PET/MRI

PET/MRI combines functional PET imaging with superior MRI soft-tissue contrast and reduced radiation exposure. Potential advantages include evaluation of liver metastases and pancreatic cystic lesions, and imaging of younger patients and long-term follow-up, though cost, availability, and examination time remain limitations.

Theranostics

One of the most exciting future developments is theranostics, in which the same molecular target is used for both imaging and therapy. Potential applications include FAP-targeted radionuclide therapy, integrin-targeted therapy, and personalised molecular treatment strategies — all currently investigational in PDAC.

Frequently Asked Questions

Q Is PET/CT recommended for every patient with pancreatic cancer?

No. PET/CT is not recommended as a routine first-line investigation. It is most useful in selected patients where the results are expected to influence management.

Q Can PET distinguish pancreatitis from pancreatic cancer?

Not reliably. Both inflammatory and malignant lesions may demonstrate increased FDG uptake. Interpretation should always incorporate CT morphology, MRI, laboratory findings, and histopathology when indicated.

Q Does a high SUV confirm pancreatic cancer?

No. SUV reflects metabolic activity, not malignancy. Infection, inflammation, and autoimmune pancreatitis can also produce high FDG uptake.

Q Can PET detect very small liver metastases?

Sensitivity decreases for lesions smaller than approximately 1 cm. Contrast-enhanced MRI remains superior for detecting small hepatic metastases.

Q Is PET useful after Whipple surgery?

Yes. PET/CT is particularly valuable when recurrence is suspected but postoperative CT findings are equivocal.

Q Can PET assess vascular invasion?

No. High-resolution contrast-enhanced CT remains the preferred modality for evaluating arterial and venous involvement.

Q Is FAPI replacing FDG?

Not currently. FAPI is a promising investigational tracer with excellent tumour-to-background contrast, but FDG remains the standard of care until larger prospective studies and guideline endorsements become available.

High-Yield Clinical Pearls

• CT is the anatomical gold standard.
• PET is the biological staging modality.
• PET is strongest for M staging.
• PET does not determine technical resectability.
• Detection of a single occult metastasis can completely change treatment.
• Declining FDG uptake generally indicates treatment response.
• MTV and TLG provide more robust prognostic information than SUVmax alone.
• PET should always be interpreted with contrast-enhanced CT and clinical findings.

Final Summary

The role of PET/CT in pancreatic ductal adenocarcinoma has evolved from a supplementary imaging technique to an integral component of multidisciplinary patient care. While contrast-enhanced CT remains the cornerstone for diagnosis and assessment of local resectability, PET/CT provides unique metabolic information that refines staging, detects occult metastatic disease, evaluates treatment response, identifies recurrent tumour, and offers valuable prognostic insight through quantitative imaging biomarkers. Emerging tracers targeting the tumour microenvironment, such as ⁶⁸Ga-FAPI, together with advances in artificial intelligence, radiomics, and theranostics, are poised to further transform molecular imaging in pancreatic cancer. As evidence continues to grow, PET/CT is expected to play an increasingly important role in delivering personalised, biology-driven care while complementing — not replacing — high-quality anatomical imaging.