Immunohistochemistry is used on cell blocks constructed from cytopathology samples fixed in methanol-based fixatives, such as CytoLyt (Cytyc Corp), and on surgical pathology tissues exposed to decalcifying agents, often without technical validation. We evaluated a panel of commonly utilized antibodies in normal tissues exposed to differing preanalytic conditions as follows: CytoLyt fixation, formalin fixation followed by exposure to decalcifying agents (Leica Decalcifier I-10% formic acid or Leica Decalcifier II-5% hydrochloric acid), or standard formalin fixation. Altered expression was observed with several antibodies compared with standard formalin fixation. Specifically, there was absent or near absent expression of thyroid transcription factor 1 (TTF-1), D2-40, and CD20 in CytoLyt-fixed tissues, whereas reduced expression was observed for p63, estrogen receptor, S100 protein, CD3, calretinin, chromogranin, and synaptophysin. Absent or near absent expression of TTF-1 was also observed with exposure to hydrochloric acid, whereas reduced expression was observed for CK5/6, CK7, p63, estrogen receptor, leukocyte common antigen, CD3, CD20, and synaptophysin. Exposure to formic acid had less impact with reduced expression observed for only 3 antibodies (CK8/18, CK7, and TTF-1). The results of this study demonstrate the need to validate immunohistochemical protocols on control tissue treated in the same manner as test tissue, including CytoLyt fixation and exposure of tissue to decalcifying agents.

Erdheim-Chester disease (ECD) is a rare xanthomatous non-Langerhans cell histiocytosis which involves the marrow space of the long bones. Extraosseous sites most commonly affected include the eyes, lungs, pituitary glands, and kidneys. We report the case of a 49-year-old woman who presented with palpable breast nodules, followed by progressive soft tissue and subcutaneous disease, and involvement of the long bones, dysarthria, and dysphagia. The histopathologic features and skeletal radiography findings are consistent with ECD. This case represents an unusual presentation, which led to delayed diagnosis, as ECD of the breast has been rarely reported. ECD should be considered in the differential diagnosis of histiocytoid breast lesions, including fat necrosis and histiocytoid invasive mammary carcinoma.