To evaluate whether PI3Kδ and/or PI3Kδ-S splice variant can serve as a potential biomarker, a series of patient samples and cell lines derived from PCa, breast cancer, colorectal, lung and/or pancreatic cancers were subjected to IHC, western blot, and RT-PCR assays for examining the expression profiles of PI3Kδ/PI3Kδ-S and PIK3CD-L/PIK3CD-S at protein and mRNA levels, respectively. The gene discussed is PIK3CD; the disease is breast carcinoma.