Distinction between isolated tumor cells and micrometastases in breast cancer: is it reliable and useful?

Background: In routine practice, the distinction between isolated tumor cells (ITC) and micrometastases (MIC) in patients with breast cancer is sometimes difficult to discern. The authors assessed differences in classifying patients according to the American Joint Commission on Cancer (AJCC) and the International Union Against Cancer (UICC) definitions and method of sizing.
Methods: We assessed the characteristics of metastatic deposits in only 1 involved lymph node in 337 patients with operable breast cancer (median follow-up, 15.3 years). When sizing multiple clusters, either the diameter of the area with close clusters (Method 1) or the size of the largest cluster (Method 2) was taken into account. Patients were classified and their survival was assessed according to the 2 sizing methods and the criteria used for definitions (size in AJCC; size and topography in UICC).
Results: With the AJCC definitions, 32 patients would be differently classified according to the method of sizing. With the UICC definitions, some patients with parenchymal ITC would be classified as pN1mi, 38 by Method 1 and 53 by Method 2. Some pathologists would classify the 66 patients who had isolated capsular vascular invasion as pN0. Classification was uncertain in 136 (40%) to 151 (45 %) patients. Survival was not significantly different between pN0(i+) and pN1(mi) patients.
Conclusions: The distinction between ITC and MIC was often difficult and without any prognostic significance. Precise guidelines are more useful for staging than for therapy. Thus, complete axillary dissection is usually performed in pN0(i+) and pN1(mi) patients, whereas chemotherapy is not indicated or debatable when MIC is the only 1 pejorative criterion.