Introduction: Many biological markers are used as prognostic and predictive indicators in invasive breast
cancers management. Among them, tumour size, grade, patho-morphological subtype, hormone receptors
status and HER2 receptor expression in addition to Ki-67 proliferative index. Also, they play a key role in
adjuvant treatment decision making. Our aim was to evaluate the association between Ki-67 proliferative
index and breast cancer immunological subtype.

Material and methods: A total of 515 early invasive patients were enrolled, tumour biological characteristics
as histopathological subtype, immune-histo-chemistry (ER,PR,HER2) status and Ki-67 proliferation index
values have been collected. The Ki-67 index level of 20%, was used as the cut-off point to differentiate
between low and high Ki-67 expression levels. Statistical analysis has been performed using the Chi
square test online tool.

Results: In this cohort, about 42%, 33%, 7%, and 18% of the cases were grouped as luminal A-like, luminal
B-like, HER2 enriched subtype, and triple-negative, respectively. All luminal A-like patients had Ki-67 level
less than 20%. About 3% of the cohort, are luminal B-like tumours with Ki-67 level less than 20%, where
30.3% of the patients were luminal B-like tumours with Ki-67 level ≥ 20%. In HER2 enriched subtype, Ki-
67 of < 20% level seen in 1.9% of cases, and Ki-67 levels ≥ 20% was observed in 5.2% of the cases. In
the triple-negative group, Ki-67 was 20% or higher in 16% of cases, and only 1.7% of patients had Ki-67
level less than 20%.

Conclusion: Luminal A-like tumours were the most frequently encountered subtype, they have low Ki-67
levels and are known to be of a low histological grade tumour, and usually associated with a good prognosis.
Also, data indicates that high Ki-67 levels are seen more often in Luminal B-Like breast cancers as
well as in triple-negative breast cancers and HER2 enriched tumours.