Benign osseous metaplasia of the breast infiltrated by invasive pleomorphic lobular carcinoma: A case report

Abstract

Introduction and importance: Benign osseous metaplasia (BOM) is a rare entity, with only few cases reported in the breast. Here we present an unusual case of pleomorphic lobular carcinoma of the breast infiltrating BOM, discuss potential mimics and review the literature.

Case presentation: An 86 year-old female presented with right breast lump for two weeks. Clinical examination revealed a palpable mass, associated with skin tethering and nipple inversion. Mammography and ultrasound showed a densely calcified lesion associated with parenchymal distortion. Core biopsy confirmed malignancy and the patient underwent mastectomy and sentinel lymph node biopsy. Histological assessment showed a 45 mm mass of benign bone trabecula infiltrated by invasive grade 2 lobular carcinoma of classic and pleomorphic types with nodal positivity (2/2). The patient received adjuvant radiotherapy to chest wall and axilla for 3 months. She remains well on aromatase inhibitors after 9 months of follow up.

Clinical discussion: Few cases of breast BOM have been reported in the literature commonly in association with benign lesions such as fibroadenomas. So far, only two cases associated with invasive classic lobular carcinoma have been reported in the literature. The main differential is metaplastic (mesenchymal/ matrix producing) carcinoma, in which the osseous component is malignant and the cancer if often of a high grade, basal phenotype.

Conclusion: We present the first case of BOM of the breast associated with invasive pleomorphic lobular carcinoma. Awareness of the entity and distinction from metaplastic carcinoma and malignant phyllodes with heterologous element are important to ensure appropriate patient management.

Keywords: Breast cancer; Osseous metaplasia; Pleomorphic lobular carcinoma.

Fig. 1

Radiological findings of the right breast lesion. A, B: Mammogram, craniocaudal and mediolateral oblique views, showing large dense and lobulated calcifications in the outer and central part of the breast. C, D: Ultrasound images showing lobulated calcifications with hyperechoic outline and dense posterior acoustic shadowing. D shows a subtle hypoechoic change (red arrows) adjacent to the dense calcification (yellow arrow). E, F: Computerized tomography (CT) scans showing a calcified lobulated lesion. F is a magnified image showing the heterogeneous osseous nature of the calcifications. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

Fig. 2

Macroscopic and microscopic appearances of the lesion with the immunohistochemical profile. A: Macroscopic image showing the hard bony and calcified breast mass (red arrows). B, C: Low and high power views for the mature bone trabecula lined by osteoblasts. D: The invasive pleomorphic and classic lobular carcinoma. Note the dyscohesive lobular cells growing in linear cords and single cells. E: The decalcified bony trabecula are infiltrated by carcinoma cells. F: A sentinel lymph node with a large metastatic deposit of invasive carcinoma. The invasive carcinoma is GATA 3 positive (G), oestrogen receptor positive (H), e-cadherin negative (I) and beta catenin negative (J) confirming the lobular phenotype. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)