ASCR Journal

Introduction

Accessory breast tissue is present in 0.6-6% of the female population, and in 0.003-0.006% of the male population and can present all the pathological conditions that can affect it as an organ, as it can contain all the components of the normal breast tissue [1-5]. Breast cancer can occur in this type of tissue and represents 0.3-0.6% of all breast cancer cases and is characterized as ectopic breast cancer [2]. Due to delayed diagnosis, and even earlier metastasis to the regional lymph nodes, it tends to have worse prognosis than orthotopic breast cancer [6]. Additionally, higher rate of malignant transformation has been reported, with stagnation in the ductal lumen being a possible risk factor [4,7,8]. Such tumors are usually found along the milk line, from axilla to groin, but can also be found in other areas such as vulva, thighs, anus and even face, with axilla being the most common site [1,9,10].

Diagnosis can be challenging as symptoms are not typical, and the locations of these tissues are not included in routine mammography and ultrasound [11]. Additionally, the development of breast cancer in ectopic breast tissue in the axilla can make the differential diagnosis between tumor and other benign pathologies such as enlarged lymph nodes, abscesses, lipomas, etc very difficult, which can lead to delay in diagnosis and treatment [2,12,13].

Case Report

A 58-year-old Caucasian woman, with insignificant medical and surgical history, visited our Surgical outpatient department for regular screening examination. Clinical examination revealed a palpable epidermal inclusion cyst-like mass of the right axilla, which was already scheduled for excision elsewhere. Mammography revealed a nodule of the upper left quadrant of the left breast with benign characteristics and without alterations in comparison to previous tests and bilateral axillary lymph nodes with benign characteristics. Further investigation with U/S was advised and re-evaluation with the results. The patient visited our outpatient department with the results of the excisional biopsy which revealed invasive ductal carcinoma, suggestive of ectopic breast cancer of the right axilla. Immunohistochemical evaluation had not been performed. The patient was admitted for further investigation with magnetic resonance mammography which did not reveal any significant findings. The specimen was re-evaluated confirming a grade 2 ductal carcinoma, while immunohistochemical report was positive for estrogen (ER) and progesterone (PR) receptors, and negative for human epidermal growth factor (HER-2), with 20% Ki-67 proliferation index.

The patient underwent additional excision for clear margin resection and axillary sentinel lymph node biopsy, after discussion in the Tumor Board Meeting. Initially the patient underwent pre-operative lymphoscintigraphy with technetium-99mtc Sulphur colloid injection around the nipple. Intraoperatively, an elliptical incision on the right axilla was performed, including the scar of the previous operation, and the tissue surrounding the previous tumor was removed. With the use of a gamma-probe and LigaSureTM exact dissector, one sentinel lymph node was identified and removed (a). Additionally, a palpable lesion near the skin was identified, which was considered suspicious for infiltration, and was also removed (b), along with the scar tissue surrounding the previous excisional site (c). The 3 specimens were sent for histopathology examination which revealed: a) breast tissue with in-situ ductal carcinoma (DCIS), 1.9cm in diameter, b) breast tissue within the subcutaneous area, in which grade 1 infiltrating ductal carcinoma and DCIS were identified with perineural invasion, and c) scar tissue with site of DCIS and infiltrative ductal carcinoma on the side of the tumor, resected in clear margins. Immunohistochemistry revealed diffuse positivity in ER and PR (more than 90%), negative Her-2 receptors, and 20-30% Ki-67 proliferation index. Margins were positive.

The case was discussed again in the Tumor Board Meeting for further treatment planning. The patient underwent radiation of the breast with radiation boost at the axilla, along with oral hormone therapy medication (letrozole 2.5mg QD). The patient is currently under follow in the outpatient department.

Figure 1: Distribution of ectopic breast cancer location.

Figure 2: Distribution of histopathologic type of cancer, among patients with ectopic breast cancer. NST Non-specific type carcinoma.

Discussion

A thorough literature review revealed 299 cases of ectopic breast cancer (Table 1). Most of the cases (97%) presented in women, from 24 to 84 years old, with a mean age of 59 years old at time of diagnosis, while men constituted the rest 3%, with a mean age of 69 and a range from 60 to 81 years old at time of diagnosis. The most common site of ectopic breast cancer was the axilla, representing 73.24% of the cases, followed by vulva, sternum, perimammary area, subclavian area, anterior chest wall, perineum, and suprapubic area (Figure 1). The most common histological type of cancer was invasive ductal carcinoma (48.60%), followed by invasive lobular carcinoma (32.40%), adenocarcinoma, mucinous carcinoma, medullary carcinoma, apocrine carcinoma, and non-specific type carcinoma (Figure 2). Out of 53 patients with available immunohistochemistry data, 46 were positive for ER/PR receptors (86.79%), while 8 out of 30 patients had positive Her-2 receptors (26.67%) [2,4,6,8,9,11-64].

Ectopic breast tissue represents an unusual entity and the development of cancer at these sites is even rarer, constituting a problem that is easily overlooked. Most of the patients develop cancer along the milk lines which can aid to the diagnosis. Breast tissue can appear however in other areas as well, highlighting the need for thorough examination and investigation of every suspicious lesion, as well as the need for histopathological examination of every lesion removed, even if they are suspected to be benign by clinical features.

In the current case, the patient was advised to undergo further investigation of the palpable lesion, despite the lesion having clinically benign characteristics. The patient however underwent excision in another hospital which could have led to miss-diagnosis with significant impact in her survival, if the lesion hadn’t been examined microscopically.

Additionally, ectopic breast tissue can appear in more than one area and can be diffusely scattered within the area. As such, ectopic breast cancer could turn out to be more complex than initially thought to be. Therefore, such cases should be referred to organized breast cancer centers that deal with these entities and be closely monitored.

Acknowledgements: The publication of the manuscript was supported financially by Anastasios Mavrogenis S.A.

Ethics: This manuscript is in accordance with General Data Protection Regulation (GDPR). As this is a case report for a patient that underwent routine surgery, no ethics committee approval was required.

Conflict of interest: The authors declare that there is no conflict of interest.

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