Several scientific reports showed that, even though the two cell lines share several common characteristics, as both are considered Basal-Mesenchymal TNBC cell lines with a spindle phenotype, SUM159 (primary breast adenocarcinoma) has mutations in HRAS and PIK3CA (https://web.expasy.org/cellosaurus/CVCL_5423), while MDA-MB-231 (pleural effusion) has deletions in p14ARF, p16, and CDKN2, and mutations in the KRAS, BRAF, and TERT promoter (https://web.expasy.org/cellosaurus/CVCL_0062), supporting the heterogeneity observed in TNBC [12,45,46,47,48]. The gene discussed is PIK3CA; the disease is breast adenocarcinoma.