ESR1 and neoplasm: In summary, they recommended that core needle biopsies should be preferred for testing if they are representative of the tumor, cold ischemia time should be kept to less than 1 hour, and samples should be fixed in 10% neutral buffered formalin (NBF; formalin in water, 10% by volume, pH 7.4) no less than 6 hours and no more than 72 hours to comply with the panel recommendations for ER and PR testing.