Early diagnosis and better treatment protocols have led to significant improvements in disease free and overall survival following a diagnosis of cancer. It is therefore becoming increasingly common for patients to be diagnosed with a second primary tumour in their lifetime, particularly in patients with primary malignant melanoma [1
]. The possible explanations include familial factors, the increasing natural lifespan of patients, and improved outcome following previous cancer treatment.
The primary breast cancer in our case did not contain melanoma cells that might have arisen through collision between two histologically different primary tumours, nor was there any pathological evidence of metaplasia, neuroendocrine differentiation or cancer to cancer metastases. The presence of two metastatic cell phenotypes in the axillary lymph node with different immunohistochemistry profiles is likely to have occurred in a metachronous fashion with the melanoma metastasis being detected incidentally during axillary dissection for breast carcinoma. The involved lymph node in probability represented the true sentinel node draining the skin of the chest wall and the breast. It is possible that melanoma micrometastases was dormant in the axillary lymph node and did not progress to clinical significance following the melanoma diagnosis. Melanoma micrometastases may therefore not be prognostically equivalent to overt nodal metastases and may reflect the natural history of melanoma micrometastases in the sentinel lymph node [9
]. Barnhill et al [10
] demonstrated that melanoma micrometastases lack significant rates of proliferation, apoptosis and neo-vascularisation when compared with macrometastases as the angiogenic and lymphangiogenic factors may be suppressed by host immune responses.
Subsequent management and follow-up of patients such as ours depend on the competing risks and natural history of the two separate primary cancers. In this case, adjuvant breast cancer treatment was of priority with continued surveillance of the melanoma.
The common sentinel node draining the breast and the trunk skin probably reflects the dominant lymphatic pattern of ectodermal structures and adds to the anatomical evidence to support the concept of the first draining node to a regional basin. The application of new technologies to cancer staging has to be guided by the natural history of the various cancer types. Detection of regional metastases has different prognostic implications for breast cancer and melanoma and management decisions need to be made on evidence based clinical criteria rather than any incidental findings.