Clinically node-negative invasive lobular carcinoma of the breast showing multiple lymph node metastases

A 73-year-old woman was pointed out of her right breast tumor on screening computed tomography (CT). Mammography showed distortion of the mammary gland and skin retraction. Ultrasound (US) showed an irregular tumor with hyperechoic haloes adjacent to the anterior tumor borders. Neither lymphadenopathy nor image findings suggesting lymph node metastasis were detected on US and CT. Core needle biopsy pathologically showed the tumor to be invasive lobular carcinoma. Under the preoperative diagnosis of node-negative breast cancer, the patient underwent mastectomy and sentinel node biopsy. Due to no sentinel node detection, a small but hard lymph node was identified and submitted for frozen section as a sampling node. After confirming the lymph node metastasis on frozen section, axillary lymph node dissection revealed 12 lymph node metastases. Postoperative pathological study showed cancer cell infiltration to the dermis near the nipple-areolar complex. In addition, immmunostaining showed the tumor to have low proliferative biology, i.e., Ki-67 labelling index of 10%. Breast surgeons should note that indolent invasive lobular carcinoma with cancer cell infiltration to the skin near the nipple-areolar complex can have multiple lymph node metastases even though showing neither lymphadenopathy nor image findings suggesting lymph node metastasis.