Cancer in the dermis of the breast has a poor prognosis. The breast dermis can 
become malignantly involved primarily in inflammatory breast cancer, through the 
direct extension of locally advanced breast cancer, or metastatically from an 
underlying breast mass or a distant primary malignancy (e.g., gastric 
adenocarcinoma). Breast dermal metastases have the shortest median survival 
among them. Breast dermal metastases are classified into eight 
clinicohistopathologic groups, one of which is carcinoma en cuirasse. We present 
a case of a 52-year-old female with a history of invasive ductal carcinoma, 
Stage IIIC (pT2N3a), treated with lumpectomy, axillary node dissection, and 
chemoradiation therapy that recurred as carcinoma en cuirasse breast dermal 
metastases. Through 18F-fludeoxyglucose positron emission tomography-computed 
tomography (18F-FDG PET-CT) and clinical images, the case illustrates the rapid 
progression and devastating consequences of carcinoma en cuirasse breast dermal 
metastases over a 4-month period despite optimal therapy. Furthermore, the case 
emphasizes the sensitivity of 18F-FDG PET-CT to detect pathology in the breast 
dermis. Finally, the case highlights the crucial role that nuclear medicine 
physicians play in helping clinical colleagues differentiate between the various 
breast dermal malignant manifestations and benign mastitis, a common confounder 
in postradiation patients.