The patient, a 59-year-old male, discovered a palpable mass on the right axillary area 10 years ago, but he did not consult a doctor for treatment. Two years ago, positron emission tomography (PET) for medical check-up revealed a lesion with increased uptake on the right axillary area of his breast. The patient had not followed up the lesion until a month ago, when he underwent an excisional biopsy at another hospital due to an increase in the size of the mass. The biopsy, followed by histology, showed signs of carcinoma (primary or metastatic), and the patient visited our hospital for further evaluation. The patient had no history of disease other than an appendectomy 40 years ago. He had a 21-pack-years smoking history, and his father had died of gastric cancer. A mildly tender palpable node was detected during a physical examination, and no symptom was found on the breast. A pigmented nevi of less than 1 cm size was found on the left auricular area and the right anterior chest of the patient. A review of the results of the histopathology of the patient from the other hospital revealed signs of metastatic carcinoma, thought to have originated from the breast. In addition, the patient's immunohistochemistry showed the following signs: estrogen receptor (+, Allred score 7), progesterone receptor (+, Allred score 6), c-erbB-2 (1+), focally positive BRST-2, and S-100 (-). Only the right axillary metastatic lymph node was found without any suspicious lesion on the breast and any accessory or ectopic breast in the mammography, breast ultrasonography (US), breast magnetic resonance imaging (MRI), and PET that were performed in our hospital (Figure 1). No sign of malignancy was observed in the chest-computed tomography (CT), ostiomeatal unit CT, abdominal US, esophagogastroduodenoscopy (EGD), and colonoscopy. All the tumor markers, such as serum AFP, CEA, PSA, CA 19-9, and CA 15-3, were within the normal ranges. A biopsy followed by histopathology was performed on the pigmented nevi that were found on the left auricular area and the right anterior chest. Signs of an intradermal nevus were found, but there were no signs of skin cancer such as melanoma. Based on all these test results, the patient was diagnosed with occult breast cancer, and a right breast skin-sparing mastectomy with axillary lymph node dissection was performed. During the surgery, no abnormality was found on the breast, but two to three 1 cm sized lymph nodes were found at the axillary level I, which were suspected to have been metastatic. The histopathology after the surgery revealed only a fibroadipose tissue without a malignant lesion on the breast and an accessory breast tissue. Two of the 29 dissected axillary lymph nodes showed signs of metastasis (Figure 2). The patient was discharged without any complication after the surgery, and subsequently underwent adjuvant chemotherapy (doxorubicin and cyclophosphamide, 4 cycles+docetaxel, 4 cycles). The patient is currently on tamoxifen (20 mg/day) and is being followed up in outpatient visits without any signs of recurrence.

A 45-year-old patient, who had discovered that he had a left axillary palpable lesion 2 years ago and had not seen a doctor about it, visited our hospital for further evaluation after an abnormality was found in his left axillary excisional biopsy 2 weeks before the visit. The patient had no history of cancer or other diseases, and had no family member who had been diagnosed with cancer. The patient was a non-smoker and was only a social drinker. In a physical examination, no abnormality other than a wound from the excisional biopsy was found in the left axilla, and no mass or suspicious skin change was detected on the breast. A review of the results of the histopathological examination performed at another hospital revealed a sign of adenocarcinoma, and the immunohistochemistry showed the following signs: TTF-1 (-), CK20 (-), and CEA (+). In the mammography, breast US, and breast MRI exams, no suspicious lesions on the breast or signs of lymphadenopathy on the axilla were observed. In addition, there was no evidence of accessory breast or ectopic breast on the axilla. The PET, chest CT, abdominal CT, and EGD exams, which were performed to determine the origin of the carcinoma, did not reveal any malignant lesion. In the right thyroid lobe, the thyroid US revealed a 0.5 cm-big hypoechoic nodular lesion that was suspected to have been malignant, but the fine needle aspiration cytology confirmed that the lesion was not malignant. In addition, all the tumor markers, such as serum CEA, PSA, CA 19-9, CA 15-3, and calcitonin, were within normal ranges. Based on all these results, the patient was diagnosed with occult breast cancer. Left axillary lymph node dissection (levels I and II) was performed on the patient, but not mastectomy. The post-surgery pathology revealed that four of the 26 dissected lymph nodes had signs of metastatic adenocarcinoma, and the immunohistochemistry showed the following results: estrogen receptor (+, Allred score 7), progesterone receptor (+, Allred score 7), c-erbB-2 (-), Ki-67 (1+), CK5/6 (-), epidermal growth factor receptor (-), and BRST-2 (+) (Figure 3). The patient was discharged without any complications after the surgery and subsequently underwent adjuvant radiation therapy on his remaining breast and adjuvant chemotherapy (doxorubicin and cyclophosphamide, 4 cycles+docetaxel, 4 cycles). He is currently on tamoxifen after adjuvant chemotherapy, and is being followed up in outpatient visits without any signs of recurrence.