Searching for a link between Ki-67 values and HER2 absence in 297 patients with triple-negative breast cancer.

Abstract

e12551 Background: Based on the report that in ER- invasive breast cancer (IBC) patients, the absence of HER2 might be linked to their Ki-67 values ( Kurbel et al. BMC Cancer 2017;17:231), this relation was searched in 297 consecutive IBC patients with triple negative tumors, treated at two Croatian hospitals. Methods: All 297 patients had ER and PgR negative IBC, The HER2 expression was IHC absent in 211 pts.; IHC 1+ in 62 pts.: IHC 2+ & ISH negative in 24 pts. Based on the cited reference that the Expectation maximization clustering (EM) of the pooled IBC Ki-67 values detects three clusters, regardless of the tumor type, the same approach was used. Differences in the distribution of HER2 values were tested by the χ2 test. Results: Three EM clusters were detected among the pooled Ki67 values: LMA (low mitotic activity) cluster: 109 cases with Ki-67 < 44%; IMA (intermediate mitotic activity) cluster: 96 cases, Ki-67 from 44 to 70% and HMA (high mitotic activity) cluster: 92 cases, Ki-67 > 70%. Beside the Ki-67, distribution of HER2 values was dependent on the age (Chi-square: 25.0309, df = 12, p = 0.014677), as shown here: In patients younger than 46, the HMA cluster was 32% larger than expected. Out of 29 HMA pts, 24 had HER2 absent tumors (53% more than expected). In patients aged 46 to 55, the IMA cluster was 27% larger than expected and out of 30 IMA, 24 had HER2 absent tumors (43% more than expected). In patients older than 55, the LMA cluster was 21% larger than expected, due to more patients with tumors positive for HER2. Out of 68 LMA pts., 22 pts. had tumors with HER2 expression (1+/2+), 40% more than expected. Conclusions: HER2 absent triple negative IBCs might be biologically different from the triple negative and HER2 1+/2+ tumors. The former were linked to pts younger than 55 and Ki-67 values > 43%. The latter showed opposite affinities, age above 55 and Ki-67 < 44%. Based on this, the absence of HER2 in triple negative IBC seems a valid target for future research.[Table: see text]