Hypotheses about the possible carcinogenic effects of ASBs in humans come from carcinogenicity observed in rodent studies. However, carcinogenic effects like those seen in rodents have not been seen in humans. 4-methylimidazole (4-MEI), which is what gives cola its brown color, was associated with cancer in extremely large doses in rodents but does not appear to be carcinogenic in humans at the moderate doses found in ASBs.[1]
A tenuous association has been found between leukemia and ASB intake. However, there is not yet a lot of evidence to support this association; the evidence to date is from small studies that are not conclusive.[2][3]
Obesity-related cancers are not associated with ASB intake.[4][5][6][7]