SIRT6 and neoplasm: A non-significant trend towards an increase in the number of apoptotic tumor cells per field was observed as a result of Sirt6 heterozygous deletion [5.7 ± 1 and 7.3 ± 1 in MMTV-PyMT+/−; Sirt6+/+ (n = 6) and in MMTV-PyMT+/−; Sirt6+/− (n = 4) mice, respectively; P = 0.13].