Breast carcinoma arose in or in conjunction with microglandular adenos
is (MGA) in 14 of 60 (23%) patients with MGA listed in the authors' fi
les. This article describes the clinicopathologic and immunohistochemi
cal features and prognosis of these carcinomas. The median patient age
was 47 years (range, 26-68 years). All patients had a mass. Six (43%)
had a family history of breast carcinoma. Lymph node metastases were
found in 3 of 11 axillary dissections. Ten patients treated by mastect
omy were recurrence-free, with a median follow-up of 57 months (range,
3-108 months). Two of three patients treated by excisional surgery we
re recurrence-free 12 and 105 months later. The third woman had bone m
etastases at 51 months and was alive 98 months after treatment. Carcin
oma arose in the MGA in 13 patients. In these patients, in situ carcin
oma was found in expanded MGA glands composed of cells with vesicular
poorly differentiated nuclei. One patient with benign MGA had carcinom
a develop in the opposite breast that was not associated with MGA. Whe
n it arose in MGA, basement membranes were present in benign MGA and i
n situ carcinoma but tended to be disrupted in invasive foci that appe
ared to be formed by coalescent MGA glands. Strong immunoreactivity fo
r cytokeratin, S-100, and cathepsin D was detected in carcinomas. Two
carcinomas had nuclear progesterone receptors, and one of these had es
trogen receptors. One carcinoma had positive findings for HER-2neu, an
d four had immunoreactivity for p53 protein. The following conclusions
were drawn from these observations: (1) carcinomas arising in MGA hav
e a distinctive histopathologic pattern; (2) the carcinomas are compos
ed of epithelial cells (cytokeratin positive, actin negative) that are
strongly immunoreactive for S-100 protein and cathepsin D; and (3) wi
th a median followup of nearly 5 years, patients with these carcinomas
had a relatively favorable prognosis, despite histopathologic and imm
unohistochemical features usually associated with a poor prognosis.