Phenotype variants of invasive breast cancer differ in associations between the primary tumor size and its Ki-67 value.

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e12588 Background: Epidemiological studies report that Ki-67 values are higher in larger invasive breast cancers (IBC). This relation was investigated in 1040 consecutive IBC patients with various immunohistological phenotypes (ER+/-; HER2 0, 1+ to 3+), all treated at a single Croatian hospital. Methods: A scatter plot of 1040 Ki-67 values with their cancer diameter (in cms) have produced an LOWESS nonparametric curve that almost overlapped with the logarithmic function of the same data set (Ki-67% = 18.39+20.63*log(D), where D is a tumor diameter in cm). The next step in using this logarithmic function as a model, was to convert D values into log(D) for linear correlations, amenable to tests of significance. Results: Among all 1040 pts, only ER positive phenotype variants Ki-67% correlated with log(D): Among ER positive tumors, the HER2 expression has decreased the correlation significance and the slope of regression lines, suggesting that the HER2 presence increases Ki67% in small tumors, while larger tumors have Ki67% less augmented than among HER2 absent tumors. Thus the highest slope of the line was found among HER2 absent ER+ patients. Conclusions: Since only ER positive tumors have shown correlation of Ki67% with the log of their tumor size, tumor biology (estimated by Ki67%) of the ER negative IBCs seems unrelated with their size. This possibly suggests that the clinical course of ER negative IBC patients is less predictable due to some etiological distinction the ER positive and ER negative breast cancers. [Table: see text]