Characterizing pseudoangiomatous stromal hyperplasia (PASH) of the breast

To investigate the associated histopathology and immunohistochemical (IHC) profile of pseudoangiomatous stromal hyperplasia (PASH) of the breast in a large, contemporary cohort.

We reviewed 193 benign breast biopsies with PASH from 185 patients without history of breast atypia or carcinoma. A tissue microarray was created and subjected to a panel of IHC. Ischemic fat necrosis was the most common finding in biopsies with PASH (181/193; 93.8%), while fibrocystic changes (170/193; 88.1%) were frequently present. PASH showed consistent, diffuse, strong staining for CD34 (193/193; 100%) and variable positivity for BCL-2 (66/193; 34.2%), SMA (47/193; 24.4%), desmin (11/193; 5.7%) and TRPS-1 (2/193; 1%), while all were negative for ERG and β-catenin. PR and ER positivity was identified in 33.7% (65/193) and 29% (56/193) of cases, respectively. Hormone receptor positive PASH was significantly associated with a higher rate of non-proliferative fibrocystic changes as compared to hormone receptor negative PASH (163/193; 84.5% vs 104/193; 53.9%, respectively) (P = 0.047). Subsequent breast atypia or carcinoma was uncommon (10/185; 5.4%), with median follow-up of 6.2 years (range 5.3-7.3 years).

ER/PR expression in PASH is less frequent than previously reported by some studies. However, the frequency of fat necrosis and associated fibrocystic changes in PASH support a chronic, hormone-related process. Consistent CD34 positivity and absence of markers seen in histologic mimics aid in the diagnosis of PASH in challenging cases. PASH does not appear to impart increased cancer risk.