A case of mucinous carcinoma of the breast in which needle tract seeding was diagnosed by preoperative diagnostic imaging.

Herein we report a 62-year-old woman with an excisable breast tumor in whom needle tract seeding was suspected during preoperative ultrasound and magnetic resonance imaging (MRI). A tumor of the right breast was observed during initial examination, and she was referred to our hospital after fine-needle aspiration cytology led to diagnosis of breast cancer, even though core needle biopsy results were negative. Mammography showed a high-density mass with a portion of the margin exhibiting very fine serrations. Ultrasonography revealed a circular mass with a border that was indistinct in some regions, and a hypoechoic band that extended from the tumor toward the skin. A mass was observed on MRI, with a linear enhancement extending on the skin side, and needle tract seeding was suspected. Fine-needle aspiration cytology revealed malignancy, and the histological appearance was consistent with mucinous carcinoma. T1cN0M0 stage I breast cancer was diagnosed, and wide excision and sentinel lymph node biopsy were performed. The skin directly above the tumor was concurrently excised to remove the biopsy puncture site. Histopathological diagnosis confirmed mucinous carcinoma, with the tumor observed to extend linearly into the subcutaneous adipose tissue in a pattern corresponding to the biopsy puncture site. The stump of the excised breast was negative for cancer cells. The possibility of tumor seeding must be considered during fine-needle aspiration cytology and biopsy. As demonstrated in this case, diagnosis of such seeding through preoperative imaging may enable extraction of the entire lesion, including the needle tract.