CDX2 is known to be a highly sensitive and specific marker for colorectal adenocarcinoma. 1 We report a case of a 64-year-old female with pT2N1a right breast invasive carcinoma of no special type diagnosed in late 2022, treated with wide local excision, axillary clearance and adjuvant chemoradiation. Surveillance imaging in early 2025 revealed extensive mediastinal, supraclavicular, bilateral hilar and left axillary lymphadenopathy, with diffuse skin thickening of the right breast. A left axillary lymph node biopsy showed sheets and clusters of malignant epithelial cells with focal discohesion, different in morphology compared to the previous tumour. There was positive immunohistochemical staining for CDX2 and CK7, but negative staining for CK20, GATA3, GCDFP, mammaglobin, ER, PAX8 and TTF1. The overall features raised concern for an upper gastrointestinal or pancreaticobiliary tract primary, but further workup including additional imaging and endoscopy were negative. Subsequent immunohistochemical staining for CDX2 was performed on the previous core biopsy and resection, which demonstrated positive staining of the tumour cells.
Thong et al. (Sun,) studied this question.