Cm. Powell et al., PSEUDOANGIOMATOUS STROMAL HYPERPLASIA (PASH) - A MAMMARY STROMAL TUMOR WITH MYOFIBROBLASTIC DIFFERENTIATION, The American journal of surgical pathology, 19(3), 1995, pp. 270-277
Pseudoangiomatous stromal hyperplasia (PASH) is frequently a microscop
ic incidental finding in breast biopsies performed for benign or malig
nant disease. However, it may also produce a mass lesion. We reviewed
PASH seen first as a tumor in 40 women aged 14 to 67 years (mean, 37 y
ears). All but one lesion were clinically palpable. The exceptional tu
mor was found by mammography. The mass, typically unilateral, was usua
lly diagnosed clinically as a fibroadenoma. Most specimens contained a
well-circumscribed tumor with a firm white-gray cut surface. In six c
ases, there was no discrete gross lesion in the surgical specimen. Mic
roscopically, there was a spectrum of pathological stromal changes ran
ging from classical PASH with anastomosing slit-shaped spaces outlined
by flat, bland spindle cells to more proliferative lesions composed o
f bundles of plump spindle cells that obscured the underlying pseudoan
giomatous architecture in the most florid lesions. The spindle cells w
ere vimentin and CD34 positive and factor VIII negative. In more cellu
lar fascicular lesions, the stromal cells acquired desmin and actin po
sitivity. These immunohistochemical features were consistent with myof
ibroblastic histogenesis of PASH. Reactivity for progesterone receptor
(PR) typically exceeded estrogen receptor (ER) in the nuclei of strom
al and glandular cells. In most lesions, the nuclei of stromal spindle
cells were ER negative. The majority of the patients were treated by
excisional biopsy. One lesion, incompletely excised, spontaneously reg
ressed. One patient had bilateral mastectomies. Follow-up was 0.6-11 y
ears (mean, 4.5 years). Five patients had ipsilateral recurrences, and
two had subsequent contralateral PASH. The morphological spectrum of
cellular proliferation and staining qualities indicates that the myofi
broblast plays a major role in the histogenesis of PASH. The pathogene
sis of PASH remains uncertain, but aberrant reactivity of myofibroblas
ts to endogenous or exogenous hormones is likely to be an important fa
ctor. Simple excision is adequate treatment initially and for infreque
nt recurrences. Diffuse PASH occasionally presents a difficult managem
ent problem that may necessitate mastectomy.