The incidence of accessory breast is 2% to 6% of the general population
]. It is the consequence of partial regression of the primitive milk streak which forms in the human embryo
]. Accessory breast tissue is seen along the milk line
] but is most frequent in the axillary region.
Embryologically being breast tissue, the accessory breast tissue is subject to homeostatic hormonal controls too and thus may become clinically apparent during puberty or pregnancy. Similarly, it is also subject to pathological changes that occur in the normal anatomical site of the breasts. There are numerous reports of masses arising in accessory breast tissue including fibroadenomas and breast cancers
]. The principal malignancy identified in accessory breast tissue, as with normal breasts, is invasive ductal carcinoma (79%), followed by medullary and lobular carcinomas which are seen in less than 10% of cases
]. Accessory axillary carcinoma is a rare form of breast cancer. In this case report, the patient had both invasive lobular carcinoma and lobular carcinoma in situ
in the accessory axillary tissue, which is an unusual finding.
This case report presents an invasive carcinoma discovered early with no lymph node involvement. The overall prognosis is similar to carcinoma of normal breast in the same tumor, node, metastasis stage, although given the location within the axillary lymph node basin, the likelihood of metastases is high
]. It is, therefore, imperative that a lump in the axillary region is triple assessed as in any breast pathology to rule out carcinoma in the accessory axillary tissue to achieve a potentially curable status. It is also important to evaluate for accessory tissue on the contra-lateral side because 13% of the cases are bilateral in normal breast
The standard UK practice is to perform MRI of the breasts in suspected or diagnosed mammographically occult invasive lobular cancer and, therefore, this imaging modality should be used if there is a high index of suspicion of carcinoma in accessory breast tissue
]. Adjuvant systemic therapy should be guided by the standard guidelines and practice (such as according to estrogen receptor (ER), human epidermal growth factor receptor-2 (HER2) status, tumor grade, stage, prognostic indices)