“…The details of included studies for the subsequent subgroup analysis are shown in Additional file 1: Table S3. Moreover, after excluding studies with the breastfeeding only as dichotomous variable, and no sufficient data of the number of cases and controls in each breastfeeding category, 23 studies were included for leukemia [ 13 , 14 , 18 , 34 – 36 , 38 – 43 , 46 , 47 , 54 , 56 , 58 , 61 , 63 , 64 , 70 – 72 ], 6 studies for lymphoma [ 14 , 33 , 36 , 40 , 43 , 46 ], and 6 studies for brain tumors [ 14 , 40 , 44 , 51 , 64 , 67 ] in dose-response meta-analysis.…”