Intranodal papillary epithelial proliferations: a local process with a spectrum of morphologies and frequent association with papillomas in the breast.

Lymph nodes, particularly those draining in major anatomic sites like axilla, pelvis, and neck are potential sites for the occasional presence of ectopic tissue, usually representative of the organ being drained. Owing to the uncertainty surrounding the processes causing such findings, and particularly in the setting of lymph node dissection and sampling for cancer staging, intranodal epithelial inclusions, rare as they may be, might be fertile soil for overdiagnosis of metastatic disease. Intranodal papillary inclusions are particularly problematic and challenging because of their complex architecture that may easily mimic a metastasis. From the files of the Breast Consultation Service, Department of Pathology at the Vanderbilt University Medical Center in Nashville, we identified 6 cases in which histopathologic examination of axillary lymph nodes revealed intranodal papillary inclusions (papillary epithelial proliferations). One case showed atypical ductal hyperplasia, 1 showed low-grade ductal carcinoma in situ, and 1 showed usual ductal hyperplasia. The corresponding breast lesions were papillomas in 5 of 6 cases, 2 of which displayed atypical ductal hyperplasia, whereas 3 showed low-grade ductal carcinoma in situ. One case showed intermediate-grade invasive ductal carcinoma, and the associated intranodal papilloma lacked atypia. Our findings suggest that intranodal papillary proliferations are often, although not exclusively, associated with papillary and noninvasive breast neoplasms, hence highlighting the origin of these intranodal lesions as independent de novo nodal processes rather than metastatic deposits.