Intramammary lymph nodes were observed in four cases, one containing metastatic melanoma from an unidentified source, one carcinoma metastatic from the opposite breast, one carcinoma metastatic from the same breast, and one containing no malignant neoplasm. A review of the literature showed lymph nodes to occur very rarely in the true intramammary location. No evidence is available as to whether the nodes observed in these cases were normally occurring nodes or if they had arisen in response to some stimulus.
Hyman LJ, Abellera RM. Carcinomatous Lymph Nodes Within Breast Parenchyma. Arch Surg. 1974;109(6):759-761. doi:10.1001/archsurg.1974.01360060029009