T-cell prolymphocytic leukemia frequently shows cutaneous involvement and is associated with gains of MYC, loss of ATM, and TCL1A rearrangement.

T-cell prolymphocytic leukemia (T-PLL) is a rare aggressive mature T-cell leukemia with frequent cutaneous presentation, which has not been well characterized. Among the 25 T-PLLs diagnosed between 1990 and 2013 at our institution, 32% (8/25) showed cutaneous manifestations, presenting as rash, purpura, papules, and ulcers. The skin biopsies showed leukemia cutis with perivascular and periadnexal irregular, small to medium-sized lymphoid infiltrates without epidermotropism.

Retinoblastoma gene mutations detected by whole exome sequencing of Merkel cell carcinoma.

Merkel cell carcinoma is a highly aggressive cutaneous neuroendocrine tumor that has been associated with Merkel cell polyomavirus in up to 80% of cases. Merkel cell polyomavirus is believed to influence pathogenesis, at least in part, through expression of the large T antigen, which includes a retinoblastoma protein-binding domain. However, there appears to be significant clinical and morphological overlap between polyomavirus-positive and polyomavirus-negative Merkel cell carcinoma cases.