Discordance of intrinsic subtype between primary tumor and lymph node metastasis in breast cancer patients.

The heterogeneity of cancer cells between primary breast tumors and lymph node (LN) metastases at the initial therapy remains unclear. This study aimed to determine whether intrinsic subtypes of LN metastasis differ from those of primary breast tumors and how much additional information is obtained. Ninety-three breast cancer cases with LN metastasis were enrolled in the study. Immunohistochemistry for ER, PgR, HER2, and Ki-67 was performed for primary breast tumors and the largest LN metastases. The intrinsic subtype was determined as luminal A (ER+, PgR+, HER2-, Ki-67 index <20%), luminal B (ER+, HER2-, PgR- or PgR+, and Ki-67 index >20%), luminal B HER2 rich (ER+, HER2+), HER2 (ER-, HER2+), and triple-negative (ER-, PgR-, HER2-). The discordance ratios for intrinsic subtypes between the primary tumor and LN metastasis were analyzed. The discordance ratios for ER, PgR, HER2, and Ki-67 were 0/93 (0%), 7/93 (7.5%), 2/93 (2.2%), and 10/93 (10.8%), respectively. The discordance ratio for the intrinsic subtype was 9/93 (9.7%). Considering the intrinsic subtype of LN metastasis, the effects of additional chemotherapy and anti-HER2 therapy could be expected in 4/93 (4.3%) and 1/93 (1.1%) patients, respectively. The discordance ratio for the intrinsic subtype between the primary breast tumor and LN metastasis was 9.7%. Considering the intrinsic subtype of LN metastasis, additional medical therapy could be expected to be effective in 5/93 (5.4%) breast cancer cases with LN metastasis. Immunohistochemistry of metastatic LNs may be useful for planning adjuvant therapy when the analysis of the primary site is inconclusive.