During embryogenesis, bilateral thickening of ectoderm from anterior axillary folds to inguinal folds, called mammary ridges or milk lines, develops into breast tissues. Only a pair in the pectoral area is spared from regression and continuously develops into normal breasts. Accessory breasts can result if the regression process is incomplete. These ectopic breasts can change physiologically and pathologically similar to normal breasts. Unsurprisingly, they are capable of turning malignant. Reported cases show the most common area for accessory breast cancer to be the axillary area. We report a rare case of accessory breast cancer over the costal ridge. We present the case of a 51-year-old Asian woman who complained of an enlarged mass lower to her left breast developed over the period of 3 months while on contraceptive pills. Unaware that the mass could be an accessory breast, the primary doctor had prescribed oral contraceptives. After our patient had noticed that the mass was obviously growing, she decided to consult a surgeon as the mass continued to grow. Expected to be benign, the mass was investigated by ultrasonography and then excised surgically. A pathology report identified the mass to be a carcinoma of the ectopic breast tissue. However, sentinel lymph node biopsy showed no nodal metastasis of all four lymph nodes. Following surgery, she received chemotherapy, radiation, and antihormonal treatment. After 2 years of postoperative follow up, she remained free of disease. This patient was diagnosed as having accessory breast cancer which presented with a subcutaneous mass. As this condition is exceptionally rare but curable by early treatments, we recommend surgeons to consider potential malignancy when patients present with a subcutaneous mass.

中文翻译：

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意外的辅助癌表现为肋cutaneous皮下肿块：一例报告

在胚胎发生过程中，从前腋窝褶皱至腹股沟褶皱的外胚层双侧增厚，形成乳腺或乳腺，形成乳腺组织。胸区只有一对幸免于退化，并不断发育成正常的乳房。如果回归过程不完整，可能会导致附件乳房。这些异位乳房的生理和病理变化与正常乳房相似。毫不奇怪，它们能够变成恶性肿瘤。报告的病例显示，辅助性乳腺癌最常见的区域是腋窝区域。我们报告了肋脊上罕见的辅助性乳腺癌病例。我们提供了一个51岁的亚洲妇女的案例，该妇女抱怨在服用避孕药的3个月内，左乳房下方的肿块增大。由于不知道该肿块可能是副乳，主治医生开了口服避孕药。在我们的患者注意到肿块明显增长后，她决定在肿块继续增长的情况下咨询外科医生。预期是良性的，通过超声检查肿块，然后手术切除。病理报告确定该肿块为异位乳腺癌。但是，前哨淋巴结活检未显示所有四个淋巴结都有淋巴结转移。手术后，她接受了化疗，放疗和抗激素治疗。术后2年的随访之后，她仍然没有疾病。该患者被诊断为患有皮下包块的副乳癌。由于这种情况极为罕见，但可以通过早期治疗治愈，