Pseudoangiomatous stromal hyperplasia with multinucleated stromal giant cells is neither exceptional in gynecomastia nor characteristic of neurofibromatosis type 1.

Six cases of gynecomastia with pseudoangiomatous stromal hyperplasia (PASH) and multinucleated stromal giant cells (MSGC) associated with neurofibromatosis type 1 (NF1) have been reported, and finding MSGC within PASH in gynecomastia has been suggested as being a characteristic of NF1. The frequency of PASH with MSGC in gynecomastia and its specificity for NF1 have not, however, been systematically studied. A total of 337 gynecomastia specimens from 215 patients, aged from 8 to 78 years (median, 22 years) were reevaluated for the presence of PASH with MSGC. Breast tissue samples of 25 patients were analyzed for the presence of an NF1 gene mutation using next generation sequencing. Rare MSGC, usually in the background of PASH, were noted at least unilaterally in 27 (13 %) patients; and prominent MSGC, always in the background of PASH, were noted in 8 (4 %) patients. The NF1 gene was mutated in only 1 (an 8-year-old boy with known NF1 and prominent MSGC) of the 25 tested patients, including 6 patients with prominent MSGC and 19 patients with rare MSGC. MSGC, usually in the background of PASH, are not characteristic of NF1.