Question: I was just diagnosed with Stage I invasive lobular carcinoma, 1.4 cm, ER/PR positive and Her2/neu negative. But my doctor told me the pathologists found some cancer cells in my sentinel lymph node, but they were so small that he said they are called “isolated tumor cells.” What does this mean?

Answer: I agree this can be a confusing situation. Isolated tumor cells means the pathologist found a few cells in the lymph node, either by routine examination under the microscope or by using special studies like immunohistochemistry, but the cells measured less than 0.2 mm. The most recent changes made to the breast cancer staging system included this category to separate it from a micrometastasis to a lymph node which means tumor cells measure between 0.2 mm and 2 mm. Unfortunately, we don’t have enough research to help us know if these isolated tumor cells behave like metastatic cancer, so they are currently classified as N0.