[A Case of Thyroid Cancer Discovered Incidentally after Breast Cancer Surgery].

The patient was a 51-year-old woman. A left breast tumor was detected during a health checkup and the patient was referred to our hospital. Upon arrival, a mobile mass measuring 17 mm in diameter was palpable in the CD region of the left breast. The mammogram showed a sawtooth mass. Ultrasonography revealed a hypoechoic mass with abundant blood flow. Needle biopsy revealed invasive ductal carcinoma. Systemic examination revealed masses in both thyroid lobes, and a fine-needle aspiration cytology diagnosis showed it to be benign. A left circular mastectomy and sentinel lymph node biopsy were performed. Pathological examination revealed a resection margin negative, ER negative, PgR negative, HER2 negative invasive ductal carcinoma, with a tumor diameter of 20 mm and 17.2% Ki-67 positivity. Thirty months after surgery, the left thyroid tumor showed a tendency to grow, and fine-needle aspiration cytology was performed again, which revealed a papillary carcinoma. A left thyroid lobectomy and lymph node dissection were performed. Pathological examination revealed that the patient had papillary thyroid cancer, T1aN0M0=Stage Ⅰ(<55y). Currently, 3 years after surgery, there is no evidence of metastasis or recurrence of either cancer.