Leukemia cutis (involving chronic lymphocytic leukemia) within excisional specimens: a series of 6 cases

We present 6 cases of chronic lymphocytic leukemia (CLL) that incidentally involved 6 excisional specimens for biopsy-proven carcinoma. CLL was notably absent from all 5 biopsies that were available for review. In 2 of 6 cases, this was the patients' initial presentation of CLL. Five of 6 cases involved routine paraffin-embedded tissue specimens and 1 case involved frozen tissue sections from a Mohs surgical procedure. The mean age range of the patients was 84 years. Only one of 5 patients in which we have follow-up data, died of a CLL-related cause at the time of this submission (mean follow-up 19.8 months). On histologic examination, the most common pattern of involvement by CLL (as seen in 4 of the 6 cases) was a dense, nodular, and superficial and deep perivascular, periadnexal, and perineural infiltrate beneath the fibrosing granulation tissue of the prior biopsy site. The infiltrate involved the upper and deep reticular dermis and subcutaneous fat. The remaining 2 cases demonstrated a novel finding of a subtle infiltration of leukemic cells among extravasated red blood cells within the mid and deep reticular dermis. In all cases, leukemic cells were present as tightly packed, small, monomorphous, hyperchromatic lymphocytes and 1 case demonstrated a proliferation center. Immunohistochemical stains were performed on 3 of 6 cases, and the leukemic cells were CD5/CD20/CD23/CD3. This case series raises awareness that CLL can incidentally involve dermatopathology specimens and occasionally be the initial presentation of the patients' systemic illness. This series also highlights the unique histologic patterns of CLL in the skin, one of which has not been previously described, and illustrates how these patterns are distinct from the typical interstitial infiltration seen in other cases of leukemia cutis.