What happened, in summary

A 53-year-old woman presented in December 2014 with a 5 cm left-breast lump and axillary swelling. Biopsy confirmed stage IIIA, grade III infiltrating ductal carcinoma that was estrogen- and progesterone-receptor negative and HER2-positive. She received four cycles of neoadjuvant epirubicin and cyclophosphamide, breast-conserving surgery, 12 weekly paclitaxel treatments, whole-breast radiation, and one year of trastuzumab completed in April 2016.

Three months later, she developed fatigue, headache, fever, and cough. CT and PET imaging showed numerous bilateral lung nodules that were initially interpreted as possible metastases. Examination of the breast and regional nodes was normal, and the imaging pattern also suggested infection. An echocardiogram found a vegetation on the aortic valve. Blood cultures then grew Nocardia, establishing disseminated nocardiosis with bloodstream infection and native-valve endocarditis rather than breast-cancer relapse.

She received intravenous meropenem and amikacin. Within two weeks, fever and fatigue improved, and the lung nodules nearly disappeared. Worsening aortic regurgitation later required prosthetic valve replacement. Prolonged antibiotics continued for eight months, with changes from trimethoprim-sulfamethoxazole to linezolid because of toxicity.

Six months after antibiotics ended, CT, echocardiography, and clinical review showed no infection relapse. She remained in good health in January 2019, and the pulmonary findings had not represented metastatic breast cancer.