Breast Tumor Disappears on Imaging During Treatment for Multiple Myeloma

What happened, in summary

A 68-year-old woman being evaluated for multiple myeloma had an incidental abnormality detected in her right breast in early 2017. Mammography and ultrasound showed a 9 mm nodule, and biopsy confirmed a well-differentiated invasive ductal carcinoma that was strongly estrogen- and progesterone-receptor positive and HER2-negative. No abnormal axillary lymph nodes were seen.

Breast-conserving surgery was recommended, but the operation was postponed for 12 weeks. During that interval, she began systemic treatment for her multiple myeloma. When she returned for preoperative localization in July 2017, the breast lesion could no longer be identified. Mammography and PET/CT also showed a complete radiologic response, so breast surgery was not performed.

She then started letrozole for the breast cancer. At regular follow-up visits, including the latest documented visit in 2022, she remained on letrozole with no evidence of breast-cancer relapse or progression. This provided about 5 years of follow-up without breast-cancer progression after the 2017 diagnosis. The breast lesion disappeared while she was receiving treatment for multiple myeloma; afterward, letrozole was the breast-directed therapy documented for the breast cancer.