Heterotopic Breast Epithelial Inclusion of the Heart
Heterotopic breast tissue on the skin along the milk line running from the axillae to the groin is well recognized as polymastia (supernumerary breast). Its reported incidence ranges from 1% to 2% (1). The unusual locations of the heterotopic breast tissue including the buttock, back of the neck, face, flank, upper arm, hip, shoulders and midline of the back and chest have been reported (1). The heterotopic breast tissue in the axillary lymph nodes has also been well recognized (2), which is often mistaken as metastatic carcinoma especially in the setting of the frozen section. However, the heterotopic breast tissue in the visceral organ has not been reported previously.
The glands seen in this case showed vaguely lobular arrangements with biphasic pattern of apical cells and basal myoepithelial cells, which was characteristic of breast ducts and glands. Although many glands consist of flattened to cuboidal cells, some glands showed columnar cells with clear vacuolated cytoplasm and apical blebs, suggestive of a pregnancy-like change. The etiology of the pregnancy-like change in the breast tissue is unknown.
Immunohistochemical stains demonstrated immunoreactivity for ER, PR, GCDFP-15 and myoepithelial markers (CK5/6, p63, D2-40, SMA), which is consistent with the breast origin.
Several epithelial inclusions have been reported to occur in the heart.
Intracardiac endodermal heterotopia (cystic tumor of atrioventricular node) is an unusual benign cystic epithelial inclusion of the heart occasionally associated with sudden cardiac death (3). This lesion is characterized by solid nests and microcystic spaces lined with epithelial-type cells with squamoid, cuboidal, ciliated or transitional appearance resembling solid cell nests of the thyroid (4). The epithelium is positive for cytokeratin, but negative for ER or PR and lacks the myoepithelial layer (4).
Mesothelial-type inclusion has also been reported in the heart such as mesothelial/monocytic incidental cardiac excrescences (MICE) (5) and adenomatoid tumor (6). In either case, biphasic pattern of the glands with negative staining for mesothelial marker (WT-1, calretinin) distinguishes breast epithelial inclusion from mesothelial-type inclusion. Cardiac myxoma occasionally shows glandular structures which are immunoreactive for various cytokeratin. However, absence of myxoid tumor component and biphasic pattern of apical and basal cells can separate breast epithelial inclusion from cardiac myxoma.
The presence of PSA, PSAP and AR immunoreactivity as well as biphasic pattern of glandular structure raise the possibility of ectopic prostate, although ectopic prostate has never been reported outside the pelvis. Intraluminal ridges and tufting usually seen in the prostate tissue were not seen in this case. Moreover, the basal cells of the prostate glands are usually not myoepithelial cells and negative for smooth muscle actin and S100, although these cells share some of the immunophenotype with myoepithelial cells, such as CK5/6, p63, and D2-40. Sclerosing adenosis of the prostate is, however, the exception and shows myoepithelial layer with diffuse actin and S100 staining. S100 staining is focal in our case and cellular spindle cell stroma characteristic for sclerosing adenosis is not seen. PSA and AR localization in the malignant and benign breast tissue has been described earlier (7) and therefore, positive immunoreactivity for PSA does not argue against the diagnosis of heterotopic breast tissue.
Introduction of the skin adnexa is also the possibility, given the history of cardiac surgery. However, diffuse distribution of the epithelium in the interstitium and epicardium occasionally intimately admixed with cardiac myocytes suggests the developmental in etiology rather than being introduced by the surgery.
The exact etiology of the heterotopic breast tissue is unknown. The most commonly accepted theory is the persistence and later development of the primordial breast tissue along the milk line in which regression should have occurred (1). This theory however cannot explain the heterotopic breast tissue outside the ventral surface such as face or back. In contrast, Hughes theory proposed that heterotopic breast tissue is caused by independently migrated nests of primordial breast cells, which locate and develop in an entirely random manner (8). This theory favors the localization of the heterotopic breast tissue near their origin with diverse pattern of distribution. Our case cannot be explained by the milk line, which is ectodermal in origin and physically distinct from endoderm-derived primitive heart tube, thereby favoring the latter theory.
This case represents the first case of heterotopic breast epithelial inclusion in the visceral organ (9).
Contributed by Sasaki, Kotaro MD; Parwani, Anil V. MD, PhD; Demetris, Anthony J. MD; Sasatomi, Eizaburo MD, PhD