Hence, we investigated the cytotoxic activity of novel thiazolinylphenyl-piperazines (2a–c and 3a-c) against LNCAP (androgen sensitive), DU145 and PC3 (androgen independent) prostate cancer cells, and MCF7 (ER+, PR+, HER2−), SKBR3 (ER−, PR+, HER2+) and MDA-MB231 (ER−, PR−, HER2−) breast cancer cell lines (Table 2). The gene discussed is ERBB2; the disease is prostate carcinoma.