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ABS CGSO study materials
ABS CGSO study resources

ABS CGSO: Diagnosis of Cancer, Including Complex Presentations and Rare or Unusual Cancers

ABS CGSO · Work through your exam, one topic at a time.

All guide sections

Diagnosis of Cancer, Including Complex Presentations and Rare or Unusual Cancers

Core concepts

Diagnosis rests on the sequence: history and risk assessment → targeted examination → imaging → tissue confirmation → staging. Candidates must know that tissue diagnosis is the default before definitive therapy, with narrow exceptions (e.g., some radiologically diagnostic tumors such as typical hepatocellular carcinoma in a cirrhotic liver, or when biopsy risks unacceptable seeding/bleeding).

Understand the difference between screening tests (asymptomatic populations), diagnostic tests (symptomatic patients), and staging investigations. Sensitivity, specificity, positive predictive value, and how prevalence changes PPV are frequent exam targets.

Complex and rare presentations

  • Carcinoma of unknown primary: requires structured workup-immunohistochemistry panels (CK7/CK20, TTF-1, CDX2, GATA3, PAX8), cross-sectional imaging, and sometimes PET-CT-before labeling as CUP.
  • Paraneoplastic syndromes (SIADH, hypercalcemia, Cushing, Lambert-Eaton) can precede the primary diagnosis.
  • Rare tumors (GIST, neuroendocrine tumors, sarcomas, lymphoma) demand specific markers (c-KIT/CD117, synaptophysin/chromogranin, desmin) and often MDT referral rather than generic chemotherapy.

Traps in questions

  • Confusing grading (differentiation) with staging (anatomical extent).
  • Assuming a normal tumor marker excludes malignancy-markers like CEA and CA-125 lack diagnostic specificity.
  • Forgetting that biopsy route matters (e.g., avoiding transcoelomic biopsy in suspected sarcoma).

Worked example

A 62-year-old with weight loss and a liver lesion: the question may tempt you to start chemotherapy on imaging alone. The rule of thumb: if the diagnosis is not radiologically certain and the patient is fit, obtain a biopsy-it changes management in a substantial minority and avoids treating benign mimics (hemangioma, abscess, focal nodular hyperplasia).