Role of nucleophosmin 1 immunostain in detecting leukemia cutis of acute myeloid leukemia with NPM1 mutation.

OBJECTIVE

The role of NPM1 immunostaining as a surrogate marker for acute myeloid leukemia (AML) with nucleophosmin (NPM1) mutation (AML-NPM1) in leukemia cutis has not been investigated.

METHODS

NPM1 immunostaining was performed using a polyclonal antibody on leukemia cutis diagnosed in 2017-2024 of 15 patients with and 15 without the NPM1 mutation. Targeted next-generation sequencing assays were performed on the initial bone marrow biopsy specimens.

RESULTS

There were 18 skin biopsy specimens from 15 patients (11 men, 4 women, 33-90 years, median: 66 years) with AML-NPM1. Thirteen (87%) patients had multiple lesions, often on the trunk and extremities. There were 8 and 10 skin biopsies done concurrently and after the bone marrow AML diagnosis, respectively. The time interval between AML-NPM1 diagnosis and leukemia cutis was 0 to 38 months (median, 1 month). NPM1 immunostaining was positive in 18 of 18 skin biopsy specimens of patients with AML-NPM1 with a leukemic infiltrate. NPM1 immunostaining was negative in 15 of 15 leukemia cutis specimens of patients with AML who had other molecular alterations not involving NPM1. The sensitivity and specificity of NPM1 immunostaining in detecting cutaneous AML-NPM1 infiltrate are 100% and 100%, respectively.

CONCLUSIONS

Although limited in number, our study shows that NPM1 immunostaining is sensitive and specific in detecting AML-NPM1-mutated cells in skin.