PIK3CA mutations have been reported to be associated with resistance to therapy in HER2+ breast cancers. This study, therefore, became imperative to determine the expression pattern of this mutant protein together with ER, PR and KI67 in order to serve as a useful predictive tool in the management of HER2 breast cancers.Methods: A total of 53 archived formalin-fixed, paraffin-embedded HER2+ breast cancer tissue blocks from 2015 to 2019 were used for the study in NAUTH Nnewi. The selected blocks

more »

... were sectioned and stained with haematoxylin and eosin staining techniques. HER2, ER and PR status confirmation as well as PIK3CA and KI67 protein expressions were evaluated using immunohistochemistry (Avidin-biotin complex method). PIK3CA and KI67 expressions in the tissue were scored based on proportion and intensity of immune-labelling using the semi-quantitative method.Result: The mean age of subjects was 47 years and the breast cancers were all invasive ductal carcinoma. Twenty-nine (54.7%) were ER+ while 24 (45.3%) were ER-. Twenty-one (39.6%) were PR+ while 32 (60.4%) were PR-. Twenty-one (39.6%) were PIK3CA negative, 9(35.8%) showed low PIK3CA, while 13(24.5%) showed high PIK3CA. Thirty-four (64.2%) were negative for KI67, 11(20.8%) showed low KI67, while 8(15.5%) showed high KI67. There was weak and moderate positive relationship between ER/PR status and PIK3CA (r=-0.032; p=0.822) and KI67 (r=0.050; p=0.721) respectively. A weak negative correlation between KI67 and PIK3CA (r=-0.118; p=0.401) were observed with 12 (22.4%) of the 13 highly positive PIK3CA cases showing either negative or low for KI67 immunoreactivity while 7(13.2%) of the 8 highly positive KI67 cases showed either negative or low PIK3CA immunoreactivity.Conclusion: This study established a moderate expression of PIK3CA mutant protein. It also pointed out an existing interesting relationship between PIK3CA and KI67, which can be further revealed in future studies.