Fluorescence in situ hybridization investigation of cutaneous lesions in acute promyelocytic leukemia

Cutaneous manifestations of acute promyelocytic leukemia are rare but well documented. Skin biopsies of leukemia can be difficult to confirm using morphology alone, and paraffin section immunophenotyping is not specific in separating acute promyelocytic leukemia from other acute myeloid leukemias involving the skin or inflammatory conditions, such as Sweet's syndrome and all-trans retinoic acid-associated genital ulcers, which may mimic leukemia cutis. Fluorescence in situ hybridization has been shown to be a fast and effective method of detecting the PML/RARA fusion gene characteristic of acute promyelocytic leukemia in fresh blood and bone marrow samples. Fluorescence in situ hybridization has also been demonstrated to be effective in detecting other chromosomal rearrangements in paraffin-embedded tissue. This retrospective study of cutaneous lesions from four patients with acute promyelocytic leukemia evaluates the utility of performing fluorescence in situ hybridization to confirm the presence of cutaneous manifestations of acute promyelocytic leukemia in formalin-fixed, paraffin-embedded skin biopsies. All patients had previous bone marrow findings of acute promyelocytic leukemia with characteristic morphology, immunophenotype, and cytogenetic studies, which detailed the presence of the t(15;17)(q22;q12) rearrangement. Two skin biopsies showed an infiltrate of blastic cells involving the dermis in a diffuse pattern and one biopsy had a perivascular/periadnexal pattern. The fourth case, involving the scrotum, showed a predominant neutrophilic infiltrate diffusely involving the dermis and epidermis with a subset of blastic cells. Nuclei were extracted from core biopsies of the formalin-fixed paraffin-embedded tissue and fluorescence in situ hybridization was performed using a dual color, dual fusion PML / RARA probe. All cases showed evidence of the t(15;17) rearrangement, with 90, 79, 51 and 16% positive signal patterns, each well above background limits. Fluorescence in situ hybridization appears to be a robust technique to detect cutaneous manifestations of acute promyelocytic leukemia in formalin-fixed paraffin-embedded skin biopsies.