Metaplastic Carcinoma in an Ectopic Breast

Manuel Caceres, MD, Jennifer Shih, Michelle Eckert, MD, Rhea Gardner, MD


South Med J. 2002;95(4) 

In This Article

Abstract and Introduction

We describe the case of an 81-year-old woman in whom a mass developed in the chest wall over 3 weeks. No previous mass in that area was reported. Physical examination was remarkable only for a 13 cm painless, purplish mass in the anterior chest wall. No masses were palpable in the anatomic breasts, and no lymphadenopathy was evident. Thoracoabdominal computed tomography showed a 3.5 x 7.0 cm necrotic mass; underlying muscle invasion could not be excluded. Wide excision of the tumor and underlying fascia was done, and margins were clear. Pathology showed a metaplastic carcinoma without continuity with either anatomic breast. Adjuvant radiotherapy was initiated because of the tumor's high-grade features. Twenty-six months after resection and adjuvant treatment, the patient continues to be free of disease. Metaplastic carcinoma is an unusual pathologic finding in the anatomic breast. This is the first report of its occurrence in ectopic breast tissue.

The mammary gland develops primarily from the ectodermal layer during embryogenesis. In the sixth week of gestation an ectodermal thickening appears, extending from the axilla to the groin in the ventral surface of the embryo, forming the structure called the milk line. Under normal circumstances, this milk line regresses except in the thoracic region, where it forms the mammary ridge, which subsequently develops into normal breast tissue. Ectopic mammary tissue results when milk line remnants fail to regress during embryogenesis, and structures varying from rudimentary breast tissue to full-grown mammary glands develop.[1,2]

The term "ectopic breast tissue" refers to supernumerary breasts and aberrant breast tissue. Histologically, supernumerary breast tissue consists of an organized ductal system communicating with its overlying skin, whereas aberrant breast tissue is an island of unorganized secretory system, without any relationship to the overlying skin.[3] It has been postulated that a genetic factor is the cause.[4,5]

The incidence of ectopic breast tissue occurrence ranges from 0.6% to 6.0%. It varies with different ethnic populations, occurring more frequently among Japanese people and less frequently among whites.[3] Although the occurrence of ectopic breast tissue is low, it is reported to be more prone to malignant transformation than the normal anatomic breast.[6] In this regard, it is hypothesized that stagnation arising in the ductal lumens of the aberrant breast tissue is a promoting factor for the development of malignancy.[7]

Ectopic breast tissue is subject to the same pathologic processes affecting the normal anatomic breasts and frequently responds to hormonal stimulation associated with menses, lactation, or pregnancy; engorgement and discomfort may occur.[8] Cases of pathologic conditions occurring in ectopic breast tissue include phyllodes tumors,[2] cystic disease,[9] fibroadenoma,[10] ductal and lobular carcinomas,[11] Paget's disease,[12] and leiomyosarcoma,[13] among others. Also of interest is the finding that papillary hydradenoma of the vulva is not a sweat gland neoplasm as traditionally believed but an intraductal papilloma arising from ectopic breast parenchyma.[14]

There have been multiple reports of malignant transformation of ectopic breast tissue in various locations, including axillary, parasternal, subclavicular, scapular, vulvar, and chest wall. The majority of reports agree that the most common location is the axilla, comprising 55% to 65% of the cases reported. The most unusual locations reported are the scapula and chest wall.[3] In the cases of malignant transformation of ectopic mammary tissue, the most frequently occurring manifestation is infiltrating ductal carcinoma,[3,10] comprising 79% of all malignancies. Medullary and lobular carcinoma are both seen in 9.5% of the cases.[10] Besides these, there have been isolated reports of Paget's disease,[12] cystosarcoma phyllode,[15] and papillary carcinoma.[16]

The unique occurrence of metaplastic carcinoma in one of our patients prompted this article. Our case is one of the most unusual pathologic presentations of breast cancer. In this case, the malignancy developed in an ectopic breast located on the anterior chest wall, an uncommon location for an ectopic breast cancer. As of this writing, ours is the only report of metaplastic carcinoma occurring in an ectopic breast. The clinical features, treatment, and outcome are described, and the literature on metaplastic and ectopic breast cancer is reviewed.


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