Diagnostic Oncology, Staging, and Tumor Pathology
Core concepts
Understand the diagnostic pathway: history/exam → imaging → tissue diagnosis (core biopsy preferred over FNA for architecture and biomarkers) → pathology → staging. Know TNM principles (AJCC/UICC), the difference between clinical (cTNM), pathological (pTNM), and post-neoadjuvant (ypTNM) staging, and stage grouping. Recognise the role of sentinel lymph node biopsy, image-guided biopsy, and liquid biopsy (ctDNA). In pathology, know grade vs stage, differentiation, margin status (R0/R1/R2), lymphovascular and perineural invasion, and immunohistochemistry panels: cytokeratins (carcinoma), S100/SOX10/melan-A (melanoma), CD45 (lymphoma), CDX2 (colorectal), TTF-1 (lung/thyroid), GATA3/ER/PR/HER2 (breast). Understand predictive biomarkers (ER, HER2, PD-L1, MSI/dMMR, EGFR, ALK, KRAS, BRAF) and molecular diagnostics (FISH, NGS, PCR).
Traps
Staging questions often test whether a finding changes T, N, or M (e.g., supraclavicular nodes in breast = N3; ipsilateral separate tumour nodule = T3/T4 depending on site). Distinguish clinical vs pathological stage and whether neoadjuvant therapy was given. Do not confuse grade (differentiation) with stage (anatomical extent). Watch HER2 low vs positive thresholds and ISH amplification criteria.
Worked example / rule of thumb
Breast cancer with a 3 cm tumour, mobile ipsilateral axillary nodes confirmed positive, no distant disease: T2 N1 M0 = Stage IIB. Rule of thumb: stage drives prognosis and treatment intent; grade refines biology but does not replace stage.