MKI67 and neoplasm: SUVmax is significantly higher in ER-negative (31 studies, SMD 0.66, 0.56–0.77, P < 0.0001), PR-negative (30 studies, SMD 0.56; 0.40–0.71, P < 0.0001), HER2-positive (32 studies, SMD − 0.29, − 0.49 to − 0.10, P = 0.0043) or Ki-67-positive (19 studies, SMD − 0.77; − 0.93 to − 0.61, P < 0.0001) primary tumours compared to their counterparts.