Table 6

 Basal cell carcinoma: differential diagnoses. Morphological criteria and major immunohistochemical findings

ArchitectureCytology34βE12, p63PSAS-100 protein, SMA
PSA, prostate specific antigen; SMA, α smooth muscle actin.
Basal cell carcinoma (adenoid cystic carcinoma)Proliferation of cells arranged in various architectural patterns, showing morpho-logical criteria for malignancy (table 5)Basaloid cells with large nuclei with considerable irregularity and variable size+±
Poorly differentiated adenocarcinoma (mostly Gleason grade 5)Tumour proliferation without glandular differentiation and composed of solid sheets, cords or single cells; necrosis can be presentCells with enlarged nuclei and prominent nucleoli+
Transitional cell (urothelial) carcinomaIrregular solid nests and cords with a striking propensity for growth within ducts and aciniHigh nuclear grade with substantial nucleomegaly, nuclear pleomorphism, and nuclear hyperchromasia. Prominent nucleoli often present+
Neuroendocrine carcinomaSheets of cells, with ribbons, nesting, palisading along fibrous bands, and rosette-like structuresPolygonal, round, or spindled tumour cells with scanty cytoplasm, and hyperchromatic nuclei identical to pulmonary small cell carcinoma
Basaloid carcinoma of the rectumSolid tumour nests exhibiting peripheral palisading, sometimes with foci of mucin secretion and areas of squamous differentiationSimilar to cutaneous basal cell carcinoma+