A Case Report on Ductal Carcinoma in situ Arising from Axillary Accessory Breast Tissue

Abstract

Accessory breast tissue can appear along the mammary ridge, extending from the axilla to the groin, with the axilla being the most common site. Malignancies arising in accessory breast tissue are rare, representing approximately 0.3%–0.6% of all breast cancer cases. When evaluating accessory breasts, it is essential to apply the same management strategies used for conventionally positioned breasts. This report presents a case of ductal carcinoma in situ originating from accessory breast tissue in the axilla of a 55-year-old woman. The diagnosis was established through a comprehensive assessment involving mammography, ultrasound, and magnetic resonance imaging. Since the axillary accessory breast tissue wasn’t initially included in the routine mammography, we added an axillary tail view to evaluate the extent and morphology of malignant microcalcifications.

INTRODUCTION

Accessory breast tissue, also known as ectopic breast tissue, results from the failure of the embryonic mammary ridge to undergo normal regression. It can occur along the mammary ridge from the axilla to the groin, with the axilla being the most commonly affected site (1). Malignancies in accessory breast tissue account for 0.3%–0.6% of all breast cancer cases and typically present as axillary masses. The most common malignant type in accessory breast tissue is ductal carcinoma (2). Here, we present a case of ductal carcinoma in situ (DCIS) arising from axillary accessory breast tissue, along with imaging findings from mammography, US, and MRI.

CASE REPORT

A 55-year-old asymptomatic patient was referred to our hospital for DCIS of the left axilla and was diagnosed via US-guided core needle biopsy at a local breast surgery clinic. Mammography and breast US were performed to assess the extent of the disease. As accessory breast tissue in both axillae was not identified on routine mammography, an additional axillary tail view mammography of the left axilla was obtained. This image revealed coarse, heterogeneous microcalcifications spanning approximately 2 cm within the accessory breast tissue in the left axilla (Fig. 1A). Breast US revealed superficially located ductal changes with echogenic foci corresponding to microcalcifications, as seen on mammography. Color Doppler examination showed increased internal and peripheral vascularity (Fig. 1B). Subsequent breast MRI with contrast enhancement displayed a 2-cm oval enhancing mass in the left axilla (Fig. 1C). However, distinguishing DCIS from axillary accessory breast tissue on MRI was challenging, as the accessory breast tissue was only visible in the contrast-enhanced axial subtraction image and was not scanned in the other sequences. No definitive breast lesions were observed.

Fig. 1. Ductal carcinoma in situ arising from the left axillary accessory breast in a 55-year-old woman.

A. Axillary tail view mammography shows coarse heterogeneous microcalcifications extending approximately 2 cm within accessory breast tissue in the left axilla (arrows).

B. US reveals superficially located ductal changes with echogenic foci spanning about 2 cm in the left axilla (left, arrows). The color Doppler scan shows increased internal and peripheral vascularity (right).

C. Contrast-enhanced T1-weighted subtraction axial imaging reveals a 2-cm oval enhancing mass in the subcutaneous fat layer of the left axilla (arrow).

D. Specimen mammography shows microcalcifications within the excised accessory breast tissue.

A wide local excision was performed on the left axillary accessory breast tissue. Histopathologic examination confirmed a 2.5 × 0.9 × 0.7 cm apocrine DCIS with microcalcifications. The nuclear grade was 2, with negative surgical margins, and no invasive cancer was present. Immunohistochemical examination showed negative results for estrogen receptor (0%), progesterone receptor (0%), and human epidermal growth factor receptor 2 (score 0). Specimen mammography revealed microcalcifications within the excised accessory breast tissue (Fig. 1D). Local radiotherapy was administered to the left axilla after surgery. The patient showed no evidence of recurrence 3 months after radiotherapy.

This case report was exempt from the ethical approval in our institution. This study was performed according to the latest ethical principles in the Declaration of Helsinki (2013). Informed consent was obtained from all participants prior to the study.

DISCUSSION

During embryogenesis, mammary ridges consisting of thickened ectoderm extend from the axilla to the groin (1). Incomplete regression of the primitive mammary tissue can lead to the development of accessory breast tissue along these ridges, with less common occurrences in various extramammary locations. Accessory breast tissue may exhibit variations in the nipple, areola, or glandular components, with fibroglandular tissue in the axilla being the most frequent (2).

Diseases affecting the normal breast, both benign and malignant, can also occur in accessory breast tissue (3). Primary breast malignancies arising from accessory breast tissue are reported in 60%–70% of accessory breast tumor cases, predominantly invasive ductal carcinoma (79%), followed by medullary and lobular carcinoma (9.5%). Other rare subtypes, including cystosarcoma phyllodes, papillary carcinoma, leiomyosarcoma, invasive secretory carcinoma, and Paget disease, have also been documented (4,5,6). Accessory breast carcinoma typically presents as an axillary mass, but early detection is often challenging due to delayed clinical symptom expression. Since delayed detection of accessory breast cancer can worsen the prognosis, it is crucial not to overlook any precancerous signs or symptoms.

Evaluation of accessory breasts involves the same management strategies used for conventionally positioned breast tissues. These include a thorough clinical examination, radiological evaluation using mammography and US, and histopathological analysis (7).

The presence of clustered microcalcifications on mammography suggests breast malignancy and necessitates further biopsy. However, suspicious microcalcifications in the axillary region can be easily overlooked or misinterpreted as calcifications in the axillary lymph nodes. Additionally, as illustrated in our case, the axillary accessory breast tissue may not always be included in the imaging field of routine mammography. A mediolateral oblique view on mammography reveals the axillary tail of the breast and the inferior aspect of the axilla. Although lesions in the lower aspect of the axilla can be detected in this view, the range of the axillary region covered by standard mammography may be insufficient. In our case, the accessory breast tissue with microcalcifications was located in the upper aspect of the left axilla and thus was not covered in routine mediolateral oblique-view mammography. An axillary tail view is often helpful in such situations. Among various diagnostic tools, US may be the primary imaging modality for evaluating axillary masses. On US, accessory breast tissue appears similar to that found within the breast. This tissue can contain either purely glandular or fibrous components, or a combination of fibrous, glandular, and fatty elements. The most common US feature of DCIS arising in accessory breast tissue is an irregular hypoechoic mass with indistinct or microlobulated margins (3,4,8). If US findings are inconclusive, confirming the presence or absence of microcalcifications can help determine the likelihood of cancer in the lesion. In our case, an additional axillary tail view was useful for correlating US findings with malignant microcalcifications on mammography. MRI findings of accessory breast cancers remain unclear due to the limited number of reported cases but may include a poorly defined subcutaneous mass within accessory breast tissue, distinct from the breast parenchyma (9). MRI is generally more limited than mammography or US in evaluating cases of DCIS.

In our case, the accessory breast tissue in the axillae was not initially identified on mammography. In contrast, US revealed echogenic foci with ductal changes in the left axilla. Consequently, an axillary tail view was obtained, which showed coarse, heterogeneous microcalcifications in the left axilla, indicating the presumed in situ components. Thus, findings from the axillary tail view were essential for identifying DCIS and evaluating the extent of the disease. Several differential diagnoses should be considered when axillary masses are detected. These include axillary accessory breast cancers, breast cancers of the axillary tail, lymphomas, lymph node metastases, metastatic carcinomas, and benign lesions such as fibroadenomas and phyllodes tumors (5). In this case, we confirmed that the lesion was located in the axillary accessory breast. The superficial location of the lesion and the presence of accessory breast tissue suggested an axillary accessory breast lesion.

Despite the underreporting of accessory breast tissue on diagnostic imaging, it is important to recognize this entity because both benign and malignant breast diseases can also manifest in accessory breast tissue. Therefore, a thorough evaluation of axillary breast tissue is crucial, involving careful clinical examination, mammography, and US. Although accessory breast cancer is rare, it is one of the most common pathologies affecting accessory breast lesions. Early diagnosis is essential for improving prognosis. When malignant microcalcifications are detected on mammography or a clinically palpable mass is found in the accessory breast tissue, further evaluation, such as biopsy or close surveillance, should be performed. However, due to their location in the axillary accessory breast tissue, malignant microcalcifications may not always be detected. Adding an axillary tail view can be highly beneficial for identifying and assessing the extent of malignancy in axillary accessory breast tissue, enabling early diagnosis and timely management.