Therefore, the expression levels of the wild-type ESR1 (ERα66) and the ESR1 variants (ERαi34, ERαi45c, and ERαΔ5) transcripts encoding constitutively active ERα proteins with C-terminal truncation in non-functioning pituitary adenomas (NFPAs) were evaluated using reverse transcription-digital polymerase chain reaction. Here, ESR1 is linked to pituitary gland adenoma.