The Diagnostic Pitfalls of Invasive Breast Lobular Carcinomas Around Involuting Fibroadenomas With Coarse Calcifications: A Case Report

A 69-year-old female with an involuting fibroadenoma (FA) was referred to our hospital for detailed examination of mammographic abnormalities around the coarse calcifications. Despite the lack of meaningful findings on medio-lateral oblique (MLO) view mammography, cranio-caudal (CC) view mammography showed spiculae around the calcifications. Ultrasound showed an oval mass with indistinct margins, disruption of the anterior borders of the mammary gland, and haloes just above the disruption areas. MRI depicted an irregular mass that showed low signals on T1-weighted images, slightly high signals on fat-suppressed T2-weighted images, and a plateau pattern on dynamic studies. Under the tentative diagnosis of breast cancer around the calcified FA, we performed a vacuum-assisted biopsy of the target lesion. Pathological examination showed small atypical cells growing in linear and scattered fashions with connective tissue proliferation, leading to the diagnosis of invasive lobular carcinoma (ILC). The patient, therefore, underwent nipple sparing mastectomy and sentinel node biopsy followed by immediate breast reconstruction using the extended latissimus dorsi musculocutaneous flap. Postoperative pathological study revealed four ILC foci up to 18 mm in size around the intracanalicular type FA with massive calcifications. Immunostaining showed estrogen and progesterone receptor positivity (both Allred score 8), human epidermal growth factor receptor type 2 negativity, and a Ki-67 labelling index of 5%. The patient recovered uneventfully, was discharged on the 14th day after the operation, and is scheduled for long-term outpatient follow-up on endocrine therapy. Diagnostic physicians should note that ILCs can develop around the calcified FAs and are prone to being overlooked on MLO view mammography.