Previous studies have shown that mRNA levels of CaV1 channels subtypes CaV1.2 (CACNA1C) and CaV1.3 (CACNA1D) are highly expressed in breast cancers.[31] Consistently, the protein levels of CaV1.2 and CaV1.3 (Figure S7A–C, Supporting Information) and the mRNA levels of CACNA1C and CACNA1D (Figure S7D, Supporting Information) were detected in MDA‐MB‐231, MCF‐7, and 4T1 cells. Here, CACNA1D is linked to breast cancer.