Prognostic significance of occult axillary lymph node metastases after chemotherapy-induced pathologic complete response of cytologically proven axillary lymph node metastases from breast cancer

Background: Primary systemic chemotherapy has been a standard of care for the management of locally advanced breast cancer (LABC) patients and has increasingly been used for patients with large operable breast cancer. Pathologic complete response (pCR) of axillary lymph node metastases predicted an excellent probability of long-term disease-free and overall survival. Although the clinical significance of occult lymph node metastases in patients with breast cancer was extensively studied, their prognostic value in patients with LABC after primary chemotherapy was not known. This study evaluated the detection rate and clinical significance of occult lymph node metastases in lymph nodes that contained metastatic carcinoma at the time of initial diagnosis and converted to negative based on routine pathologic examination after primary systemic chemotherapy. Methods: Fifty-one patients with LABC and cytologically involved axillary lymph nodes that converted to negative after preoperative chemotherapy were identified from 2 prospective clinical trials. All lymph node sections were reviewed, 1 deeper level hematoxylin and eosin-stained section of each lymph node was obtained and immunohistochemical staining for cytokeratin (CK) was performed. A total of 762 lymph nodes were evaluated for occult metastases. Kaplan- Meier survival curves were used for calculating disease-free and overall survival times. Results: Occult axillary lymph node metastases were identified in 8 of 51 (16%) patients. In 6 patients, occult metastases were found in only 1 lymph node. In 7 patients, only isolated CK-positive cells were identified. In all cases, occult carcinoma cells were embedded within areas of fibrosis, foreign body giant cell reaction, and extensive histiocytosis. Patients with occult lymph node metastases tended to have a higher frequency of residual primary breast tumors than those without occult metastases (4 of 8 vs 7 of 43, respectively). There was no statistically significant difference in disease-free or overall survival times between patients with and without occult metastases after a median follow-up 63 months. Conclusions: Persistent occult axillary lymph node metastases were not uncommon in patients with axillary lymph node-positive LABC who experienced a pCR in involved lymph nodes after preoperative chemotherapy. However, such occult metastases did not adversely affect the good prognosis associated with axillary lymph node pCR. Therefore, routine lymph node CK evaluation was not recommended after primary chemotherapy.