Long term/major side-effects of laxative abuse?

i've been abusing laxatives for just under 2 years now taking up to as many as 20 a day and i was just wondering if i was doing any serious damage. I know about the dependancy and all the short term things like dehydration and electrolyte imbalace but i was wondering if there was an increased risk of any cancers or ruptures, anything along those lines. thankyou.