EXCLUSIVE

Chief Keef screwed over breast cancer patients by bailing out of a Cleveland charity concert hours before he was supposed to go on stage ... according to a lawsuit obtained by TMZ.

In court docs, Kim Productions claims it paid Keef a $15K deposit ... to perform at the RapCure cancer benefit last June. The balance -- $10K -- was supposed to be paid at the event.

Kim Prods. claims the day before the event, Keef demanded a $2,500 advance to cover travel expenses. Kim says the money was wired ... and Keef's agent claimed Keef was on his way.

According to the lawsuit ... Keef failed to show up on time ... so the concert was cancelled and ticket holders got their money back ... which meant the charity ended up in the red.

The company is suing for $26K -- the money it paid to Keef plus the amount spent on the theater, lights, equipment, advertising and the refunded tickets.