Lumbar nodule

A 57-year-old man presented with a long history of a persistent, firm raised nodule in the right lumbar area with increasing size. The patient was otherwise well, with no constitutional symptoms and no significant past medical history.

The specimen was composed of a nodule measuring 1.7 × 0.9 × 0.9 cm embedded in subcutaneous tissue with an overlying ellipse of unremarkable skin. Multiple sections of the excisional biopsy demonstrated nearly circumscribed growth of the basaloid lesion in the dermis and subcutaneous fat tissue with a surrounding pseudocapsule (Figure 1a). There was zonation between basaloid cells at the periphery with numerous “shadow” cells in a fibro-collagenous matrix with an inflammatory background (Figure 1a). Multiple foci of keratin were evident, with an associated multinucleated giant cell reaction. The tumour exhibited atypical focal features, including a very focal infiltrative pattern at the periphery (Figure 1b). Irregular foci of central necrosis (comedonecrosis) were present in several lobules (Figure 1c-d). Also, the tumour was composed predominantly of basaloid cells with a variable degree of atypia (Figure 1d) and an increased mitotic rate, up to five mitotic events/high-power field (Figure 1e). No definite vascular or lymphatic invasion was identified. The tumour was close to the surgical margins but appeared to have been completely excised.