Comparative evaluation of nuclear and histological grades as prognostic factors for invasive breast cancer

Although tumor grade, defined by either the nuclear grade (NG) or the histological grade (HG), is widely accepted as one of the prognostic factors for breast cancer, there is a limited direct comparison between these two grading systems. The object of the current study was to compare their prognostic capabilities on the same specimen in a single institutional cohort.

We collected data from 1125 patients with breast cancer who underwent surgery at Kaizuka City Hospital between 2002 and 2016 and analyzed the prognostic capability of NG and HG in comparison with other clinicopathological factors. Pathological diagnoses were performed by a single pathologist throughout the study period.

The median follow-up was 52.9 months. During the follow-up period, 103 distant recurrences were observed. The concordance rate of grades between NG and HG was 72.1%. The 5-year recurrence-free survival (RFS) rates for patients with NG1, NG2, and NG3 were 90.6%, 91.8%, and 82.2%, respectively, and the rates for patients with HG1, HG2, and HG3 were 92.7%, 88.6%, and 82.5%, respectively. Significant differences in RFS were noted among each grade for HG. However, this was not true for NG; a significant difference was not noted between NG1 and NG2. In terms of subtypes, both NG3 and HG3 were significantly associated with worse outcomes in patients with ER-positive/HER2-negative tumors.

Although not a few patients exhibited discordant results between NG and HG, both NG and HG predict outcomes for breast cancer patients, but the latter might appear to be superior as a three-grade classification scale.