[A case of mucinous carcinoma treated by local excision after long-term serial observations].

We report a case of a 45-year-old woman in whom an abnormality was identified by an examination when she was 42 years old. Breast ultrasonography revealed a cyst in the C area of the left breast. Ultrasonography performed 3 years later showed a mass lesion, 1 cm in diameter, in the C area of the left breast. Contrast-enhanced magnetic resonance imaging (MRI) showed a mass shadow. Core needle biopsy was performed, and the pathological diagnosis was mucinous carcinoma. Partial excision of the breast and sentinel lymph node biopsy were performed. The final histopathological diagnosis was mucinous carcinoma( pure type, estrogen receptor[ ER][ +], progesterone receptor[ PgR][ +], human epidermal growth factor receptor-2[ HER2][ 0], Ki67[ 10%], T1N0M0, stage I). One year after the operation, no signs of recurrence or metastasis have been observed. It was difficult to ascertain the presence of a lesion as the patient experienced pregnancy and childbirth during serial observations. An early diagnosis was made by imaging techniques such as consecutive ultrasonography, owing to which we were able to treat the patient early. The findings of this case emphasize the need for serial imaging studies.