To our knowledge, this is the first case, in the English literature, showing findings consistent with metastasis to axillary SNL, related to a metastasis to the breast from a colon adenocarcinoma.
Breast metastases from colon cancer are very rare and they are usually associated with poor prognosis, due to disseminated disease. Since their first description, in 1976 , only 20 cases have been reported so far . The majority of patients have undergone surgical excision even though breast surgery, in these cases, was aimed only at diagnosis and/or palliation. In the present case we opted for surgery, despite the presence of lung metastases, for two reasons. First, the diagnosis was not completely clear between a metastasis from colon cancer and a primary breast cancer. Second, the patient was very anxious about her breast lump and wanted it removed. She also asked for a sentinel node biopsy. Interestingly, the sentinel node turned out to harvest a tiny micrometastasis that makes this case rather unusual. Even though it is possible that micrometastasis could have been blood borne, it is more likely that colon cancer cells firstly deposited in the breast, and then, via the breast lymphatic vessels, reached the sentinel node. Accordingly, no disseminated nodal metastases were evident on CT and US before breast surgery.
The possible derivation of micrometastasis from the breast metastasis is in keeping with the general mechanism by which only a small proportion of disseminated cells become micrometastases and only a fraction of micrometastases progress to become macrometastases . Moreover, the cancer cell invasion of breast peritumoral lymphatics should suggest that metastases (or even recurrences) from solid cancers are able to further metastasize, via well-known pathways also recognized in primary breast cancer .