The study you refer to, "rats fed with GMO food had developed tumors that were as big as their original size" used Sprague-Dawley rats, typically chosen in lab studies because the breed is known to quickly develop massive tumors regardless of other factors. The results in this study were not statistically significant, and were drawn from a sample size way too small, on a type of animal that is known to develop tumors on its own.
Furthermore, the numbers in the study actually showed that male rats who consumed glyphosate in their drinking water (because simultaneously testing multiple variables on groups of like 5 rats makes sense, right?) actually lived longer than those which did not, and all rats in the study grew massive tumors, even the control group.
If you're going to base an opinion on "science", please make sure you actually read the study and have enough knowledge to determine whether it's bullshit or not.
Thanks,
Someone who actually is "pro science"