Many of the gene products deregulated in cancers such as SCLC (e.g., MYC, TP53, CCNE, KRAS, HSP90, ESR1, and NOTCH) are CCT client proteins [23], suggesting a role for the involvement of CCT in the development of cancer, driving the need to better understand its contribution to malignant transformation. This evidence concerns the gene ESR1 and cancer.