What is the role of fine-needle aspiration cytology (FNAC) in the diagnosis and management of gallbladder cancer?

Role of FNAC in Gallbladder Cancer

Fine-needle aspiration cytology (FNAC) should NOT be routinely performed in potentially resectable gallbladder cancer due to risk of tumor seeding, but plays a crucial diagnostic role in advanced, unresectable disease to confirm malignancy before initiating systemic therapy. 1

When to Use FNAC

Appropriate Indications

• Advanced/metastatic disease requiring systemic treatment - FNAC is essential to obtain tissue diagnosis before initiating chemotherapy or targeted therapy 1
• Unresectable tumors - When surgical resection is not feasible, FNAC confirms malignancy and enables molecular profiling 1
• Metastatic lesions - Sampling of liver metastases or distant lymph nodes is appropriate 1
• Ambiguous imaging findings - When radiological features are inconclusive and management depends on tissue diagnosis 2, 3

Contraindications and Cautions

Critical caveat: In potentially resectable gallbladder tumors, FNAC should be avoided or decided only in multidisciplinary settings because tumor seeding along the needle track has been reported, though the exact risk appears very low 1. The 2023 ESMO guidelines explicitly state that decisions to undertake primary tumor biopsy via any transperitoneal approach (including EUS-guided FNA) must be made carefully in multidisciplinary discussion for potentially resectable disease 1.

Diagnostic Performance

FNAC demonstrates excellent diagnostic accuracy for gallbladder cancer:

• Sensitivity: 85% 3
• Specificity: 94% 3
• Diagnostic yield: 94.6% with 90.1% positive for malignancy 2
• Cytohistological concordance: 94.4% 4

The largest series of 596 cases showed FNAC to be safe, rapid, reliable, and cost-effective with no major complications (hemorrhage, peritonitis) reported 5.

Technical Approach

Preferred Methods

• EUS-guided FNA/FNB - Allows accurate assessment of locoregional extension, vascular invasion, and lymph node involvement while obtaining tissue 1
• Ultrasound-guided FNA - Most commonly used approach for gallbladder masses, particularly in advanced disease 2, 6, 5
• CT-guided FNA - Alternative for accessible lesions

Tissue Acquisition Strategy

The 2023 ESMO guidelines prioritize obtaining adequate tissue for both diagnosis AND molecular profiling 1. For gallbladder cancer specifically:

• Core biopsy is preferred over cytology alone when possible to ensure sufficient tissue 1
• Cell block preparation from FNA material enables immunohistochemistry for subtyping 2
• Molecular testing (NGS) should include IDH1, HER2/ERBB2, BRAF, FGFR2, and NTRK alterations 1

Cytomorphological Spectrum

FNAC can reliably identify and subtype gallbladder malignancies 2:

• Adenocarcinoma NOS - 79.1% of cases
• Unusual variants (20.9%): papillary adenocarcinoma, mucinous adenocarcinoma, signet ring, adenosquamous, squamous cell carcinoma, neuroendocrine neoplasms, undifferentiated carcinoma

Common Pitfalls

1. Xanthogranulomatous cholecystitis - Can mimic malignancy both radiologically and cytologically, accounting for most false positives 5
2. Inadequate sampling - Necrotic material without viable tumor cells occurs in approximately 4-9% of cases 4, 5
3. Atypical/suspicious categories - Categories 3 and 4 (atypical cells, highly suspicious) require repeat FNA or surgical management based on radiological features 4

Algorithm for Decision-Making

For potentially resectable disease:

• Proceed directly to surgery WITHOUT preoperative FNAC
• Obtain tissue diagnosis intraoperatively if needed

For advanced/unresectable disease:

• Perform EUS-guided or US-guided FNAC to confirm malignancy
• Ensure adequate tissue for molecular profiling (NGS panel)
• Use results to guide systemic therapy selection

For equivocal cases:

• Discuss in multidisciplinary tumor board
• Consider repeat imaging or alternative biopsy routes
• If FNAC shows atypical cells with worrisome radiology, proceed to surgery or repeat sampling 4