Sarcoid-Like Granulomatosis in a Patient With Breast Cancer Mimicking Refractory Metastatic Disease.

Sarcoid-like granulomatosis is a known but rare adverse reaction to immune checkpoint inhibitors and chemotherapy in the treatment of advanced solid tumors. We present a case of a 29-year-old female with a pathologically confirmed poorly differentiated invasive ductal carcinoma of the breast with presumed metastases to the lungs, hilar lymph nodes, liver, and spleen. Despite appropriate chemotherapy, the patient developed pulmonary lesions that were interpreted on imaging studies as progression of malignancy. Autopsy revealed disseminated sarcoid-like granulomatosis with multiple noncaseating granulomata with associated fibrosis in the lungs, liver, and spleen. No residual invasive carcinoma or metastatic disease was identified. This case illustrates the difficulty in differentiating this nonneoplastic process from progressive disease in the clinical setting.