A 62-year-old male patient had a mass in his right lower abdominal wall for more than 50 years. He sought treatment due to its progressive growth for 2 years with ulceration and pus for more than 3 months. The patient found a subcutaneous mass on the abdominal wall with no obvious cause more than 50 years ago. The size of the mass was ~1.5 × 1 cm. The mass could be pushed without tenderness, and the surrounding boundary was unclear. He did not pay attention to the mass. In the past 2 years, the patient felt that the mass had progressively enlarged; its size had increased to ~3 × 2.5 cm. The texture had gradually hardened and was accompanied by pain. Three months before seeking treatment, the mass showed swelling and erosion on the surface, with purulent exudates for no obvious incentive. Physical examination: the patient’s two breasts were symmetrical, with no local bulge or erosion and no palpable mass; there were no significantly enlarged lymph nodes palpable in the bilateral axillae and both up and down clavicles. A mass was found in the right lower abdomen with redness, swelling, and erosion on the surface. The mass was ~3 × 2.5 cm in size. Its texture was hard, the boundary was unclear, and it was not movable with tenderness by pressing. B-ultrasound revealed a subcutaneous nodule in the right abdomen with a size of ~2.8 × 2.5 × 1.5 cm. On February 27, 2017, the patient underwent abdominal mass resection with local anesthesia in a local hospital. Gross examination of the mass showed that a piece of skin tissue had eroded on the skin surface, and the mass was under the incision surface of the skin with a size of 2.8 × 2.5 × 1.5 cm; the mass was gray and hard, and the boundary was unclear. Observations by microscopy were as follows: in the subcutaneous tissue, the tumor cells had large nuclei with dark staining; the chromatin was thick, and the nucleoli were obvious; pathological mitosis was shown with less cytoplasm; the tumor cells were arranged in lumps, nests, and glandular tubules in small amounts with necrosis in small amounts (). Invasive growth of the tumor tissue was observed, and its boundary was unclear; the infiltration reached the subcutaneous fibrous connective tissue and the superficial skin (), invading the vessels and nerves. The pathological diagnosis was grade II infiltrating ductal carcinoma derived from the accessory mammary gland (abdominal wall) with neuroendocrine characteristics, with the immunohistochemistry of ER (100% strong positive), PR (100% strong positive), HER-2 (−), ki67 (40% positive), Syn (+),CgA (+), and GCDFP15 (+) (–). Postoperative positron emission tomography–computed tomography (CT) showed the following: 1) changes after the tumor resection in the right lower abdominal wall, with no local residual tumor; 2) multiple retroperitoneal and pelvic nodules on both sides, with a maximal size of 2.4 × 1.8 cm, standardized uptake value (SUV)max 3.6 and SUVave 3.2, which were considered lymph node metastases; 3) multiple nodules in both inguinal regions, with the maximal size of 1.5 × 1.0 cm, SUVmax 2.7 and SUVave 2.4, which were considered lymph node metastases; 4) no obvious signs of malignant primary tumor in other parts of the body. On March 15, 2017, as shown in, CT showed postoperative changes on the right lower abdominal wall; the structure of the surgical area was disordered, and the skin was slightly thicker, with a subcutaneous patchy high-density shadow; a few lymph nodes were observed near the bilateral groin and iliac vessels; and some patchy low lesions were uneven in their internal density, including a large lesion ~1.7 × 2.3 cm in size. A definitive diagnosis of accessory breast cancer at the right abdominal wall with bilateral inguinal and peritoneal lymph node metastases in stage VI was obtained. On March 28, 2017, radiotherapy was performed with the following dosing: abdominal surgical area of the original tumor: 6 MeV electron beam, 50 Gy/25 f; pelvic area: 6 Mev-X ray, PGTV: 50 Gy/25 f, PCTV: 45 Gy/25 f. On May 18, 2017, as shown in, the CT reexamination revealed shrinkage of several enlarged lymph nodes around the bilateral groin and iliac vessels and some patchy low lesions with uneven internal density, including a large lesion ~2.0 × 1.4 cm in size. After radiotherapy, the patient was treated with tamoxifen 10 mg bid until now. The CT reexamination on August 1, 2017, as shown in, showed that multiple lymph nodes near the bilateral groin and iliac vessels were smaller than before, and some of them had low-density necrosis, with the largest one ~1.7 × 1.2 cm in size. As of this writing, the patient is in stable condition.