[Diagnosis of ductal carcinoma in situ with interruption of the anterior border of the mammary gland by ultrasonography-a case report].

We report a case of ductal carcinoma in situ( DCIS) with interruption of the anterior border of the mammary gland by ultrasonography. The patient was a 41-year-old woman. The patient was identified by a focal asymmetric density on her left breast by screening mammography. Ultrasonography showed an ill-defined low echoic mass, 25 mm in diameter, in the A area of her left breast. The tumor had features consistent with the interruption of the anterior border of the mammary gland. Therefore, she was diagnosed with invasive ductal carcinoma of the breast. We performed a modified radical mastectomy with sentinel lymph node biopsy. A resected specimen led to a diagnosis of DCIS positive for estrogen receptor and progesterone receptor, and negative for HER2/neu protein expression. After surgery, she was administered tamoxifen. One year and 6 months after the operation, she is well without metastases. Ultrasonography is generally useful to differentiate between a DCIS lesion or an invasive ductal carcinoma lesion. However, in this case, we could not diagnose the tumor as DCIS by ultrasonography because the tumor was interrupted by the anterior border of the mammary gland. This case suggests that we should be cautious when diagnosing low echoic tumors with interruption of the anterior border of the mammary gland by ultrasonography.