Introduction:Primary accessory breast cancer is rare and most commonly occurs in the axilla. Due to its low incidence, few studies have discussed axillary reconstruction after accessory breast cancer resection. In the present report, we describe a patient who underwent axillary reconstruction with a thoracodorsal artery perforator (TAP) flap after resection, and reconstruction methods after resection of axillary accessory breast cancer are discussed based on current and previous reports.Patient concerns:A 60-year-old woman presented with a 7-year history of a gradually growing lump in the left axilla.Diagnosis:The patient was diagnosed with latent breast cancer, axillary lymph node metastasis, or carcinoma of the accessory axillary breast with axillary lymph node metastasis.Interventions:After preoperative chemotherapy, tumor resection and axillary lymph node dissection were performed, followed by immediate axillary reconstruction using a TAP flap. The patient received postoperative adjuvant endocrine and radiation therapy (50 Gy).Outcomes:No recurrence or metastasis was observed for 5 years postoperatively. The reconstructed axilla was not bulky, and scar contracture was not observed, with a full range of motion of the shoulder joint.Conclusion:We described a patient who underwent immediate TAP flap reconstruction after resection of accessory breast cancer and axillary lymph node dissection, followed by postoperative radiation, which could cause scar contracture. The patient was followed up for more than 5 years after the operation and radiation therapy, and the appearance of the axilla and range of motion of the shoulder were good despite postoperative radiation.