Abstract: Objective To explore the association of 21 gene recurrence score (RS) and clinicopathologic characteristics and prognosis of axillary lymph node negative, hormone receptor (HR) positive invasive lobular carcinoma of the breast (ILC) and to evaluate the application value of 21 gene RS in ILC. Methods The clinicopathologic data of 32 ILC who underwent 21 gene RS testing from May 2012 to December 2015 was retrospectively analyzed. At meantime, 301 invasive carcinoma of no special type (NST) were selected from the same hospital as control group. Results In 32 ILC patients, low risk (RS<18), intermediate risk (18≤RS<31) and high risk (RS≥31) group accounted for 87.5%, 12.5% and 0%. While in 301 NST patients, low, intermediate and high risk group accounted for 64.5%, 26.6% and 9.0%. There were significant differences in RS between ILC and NST groups (P<0.05). Tumor grade and Ki-67 index were significantly different between the 2 groups (P<0.05 for all). After a median follow-up of 38 months, no recurrence occurred in 32 ILC and the recurrence rate of low, intermediate and high risk group in NST cohort was 3.6%, 8.8% and 11.1%. Conclusions The difference of RS distribution between ILC and NST was significant, and the proportion of high-risk group in ILC was significantly lower than that of NST. The role of RS in ILC chemotherapy decision-making remains unclear. The prognostic value of RS for ILC remains to be determined by more clinical studies.

Key words: breast neoplasms, invasive lobular carcinoma, prognosis, 21-gene assay, recurrence score