A Rare Metaplastic Breast Cancer With Bone-Like Tissue Formation

What happened, in summary

At age 82, a woman noticed a new lump in the upper outer part of her left breast accompanied by a dull ache. She had previously been treated for a separate right breast cancer 18 years earlier. Examination found a roughly 2 cm left breast mass without enlarged axillary nodes. After discussing breast-conserving surgery with radiation versus mastectomy, she chose a left total mastectomy for peace of mind and to avoid future local problems. Sentinel lymph node biopsy was performed at the same operation, and all three nodes were negative for cancer. Final pathology showed a 2.5 cm metaplastic breast carcinoma with osteoblastic differentiation, classified as T2N0. The tumour had weak oestrogen-receptor staining below 10%, was progesterone-receptor negative and HER2 negative, and was described in the report as triple-negative. BRCA testing did not identify a mutation. The unusual tumour produced an osteoid matrix, helping explain the calcified appearance seen on breast imaging. Because the expected survival benefit was uncertain in an older patient with this uncommon tumour biology, adjuvant chemotherapy was not advised. Hormone therapy was also not recommended. She recovered without notable complications. At follow-up one year after mastectomy, she remained alive with no evidence of recurrence. The left metaplastic cancer was treated as a new contralateral primary, distinct from the invasive ductal cancer removed from her right breast 18 years earlier.