What happened, in summary

This 11-year-old prepubertal girl developed a painless lump in her right breast that slowly enlarged over 8 months. Because breast carcinoma is extremely rare in children, the diagnosis was delayed. On examination, the mass occupied the entire right breast, measured about 5 × 6 cm, and was fixed to the overlying skin and underlying pectoralis major muscle. A single mobile, nontender right axillary lymph node was palpable, while the opposite breast and left axilla were normal. She had no nipple discharge, systemic symptoms, family history of breast or ovarian cancer, or known radiation exposure. Imaging did not show disease in the opposite breast or abdomen. Core biopsy diagnosed infiltrating ductal carcinoma, not otherwise specified, and immunohistochemistry showed ER-negative, PR-negative, and HER2-negative disease, making it triple-negative. Clinically, the tumor was described as locally advanced, cT4bN1M0. She underwent modified radical mastectomy using the Patey modification with level III axillary lymph node clearance. Part of the pectoralis major muscle was removed because the growth had infiltrated it. Final pathology showed infiltrating ductal carcinoma NOS, grade II. Eleven axillary lymph nodes were reactive and did not contain metastasis, giving a postoperative classification of pT3N0Mx. No adjuvant chemotherapy or radiation was described. The authors emphasized that her diagnosis was unusually rare because most pediatric breast tumors are benign and, when malignant, are often secretory carcinoma rather than infiltrating ductal carcinoma NOS. They also noted that her painless presentation contributed to late diagnosis. As of April 2014, she was tumor-free after surgery. The case is notable because pediatric breast cancer can be missed when a breast lump is assumed to be benign because of the child’s age.