A new study has reported that small lymph node metastases in lobular breast cancer patients may be incorrectly staged if the pathologist adheres to accepted classification criteria. There is low reproducibility among pathologists in classifying micrometastases and isolated tumor cells in sentinel lymph nodes in cases of lobular breast cancer.
The authors postulated that strict adherence to AJCC criteria may result in inaccurate staging of lobular breast patients who undergo lumpectomy and other breast cancer surgery that includes sentinel node biopsy.
To perform the study, the authors reviewed 51 cases of metastatic lobular carcinoma found in sentinel lymph node biopsies during the period 1998 to 2008. The authors then reassessed all sentinel lymph nodes strictly according to AJCC criteria. Completion axillary lymph node dissection among these patients and clinical follow-up were also reviewed.
The patients were originally classified as follows by the primary pathologist: 10 isolated tumor cells, eight micrometastases, 27 macrometastases, and six positive cases without further classification. Using strict adherence to AJCC criteria, the cases were assigned the following classifications by the authors: 21 isolated tumor cells, two micrometastases, and 28 macrometastases. Twelve of the isolated tumor cells cases had undergone full axillary dissection, and three (25%) were found to have had additional macrometastases.
All of the micrometastatic cases had undergone axillary dissection and all had been determined to be negative for additional cancer. Twenty-two macrometastatic cases had undergone full axillary dissection and 16 (73%) had been found to have additional macrometastases.
The authors conclude that diffuse single cells or small clusters should not be interpreted as isolated tumor cells in invasive lobular carcinoma sentinel lymph nodes. Therefore, the criteria for assessing small volume metastases in the sentinel lymph node of invasive lobular carcinoma cases need to be more clearly defined.

Comments regarding the study

It is apparent that experienced pathologists will take into account the tendency of lobular breast cancer to infiltrate in small linear groups (“Indian file”), which could otherwise result in downstaging of lobular micrometastases to isolated tumor cells. However, as the authors point out, strict adherence to AJCC criteria would frequently result in such misclassification.
It is becoming more important that the criteria be clear since there is a recent trend toward forgoing completion axillary node dissection in cases of sentinel lymph nodes that are positive only for isolated tumor cells.