Accurate classification of sentinel lymph node metastases in patients with lobular breast carcinoma

Among pathologists there is low reproducibility in classifying small volume metastases in sentinel lymph node particularly in cases of invasive lobular carcinoma. We postulate that strict adherence to American Joint Commission on Cancer (AJCC) 2003 criteria may result in inaccurate staging of lobular carcinoma patients. We reviewed cases of metastatic lobular carcinoma in sentinel lymph node biopsies between 1998 and 2008. All sentinel lymph nodes were reassessed using strict adherence to AJCC 2003 criteria. Subsequent axillary lymph node dissection and clinical follow-up were reviewed. Fifty-one patients met our inclusion criteria and were originally classified by the primary pathologist as follows: 10 isolated tumor cells, 8 micrometastases, 27 macrometastases, and 6 'positive' cases without further classification. Cases were re-classified using strict adherence to AJCC 2003 criteria as follows: 21 isolated tumor cells, 2 micrometastases, and 28 macrometastases. Twelve isolated tumor cells cases underwent full axillary dissection, and 3 (25%) had additional macrometastases. All micrometastatic cases underwent axillary dissection; all were negative. Twenty-two macrometastatic cases underwent full axillary dissection and 16 (73%) had additional macrometastases. Diffuse single cells or small clusters should not be interpreted as isolated tumor cells in invasive lobular carcinoma sentinel lymph nodes. The criteria for assessing small volume metastases in the sentinel lymph node of patients with invasive lobular carcinoma need to be more clearly defined.