Forbidden World
aka Mutant
(1982)

A Roger Corman "Alien" ripoff with a cheesy sound track, bad lighting, spastic editing, footage from other Corman movies and two (2) hot babes!  

Short Version:  
They kill the monster by feeding it a cancerous tumor.  

Long Version:  
Space Marshall Mike Colby (Jesse Vint) is awakened from suspended animation by his buddy SAM the robot, for a space battle with a pack of space pirates.   Special effects courtesy of footage from Corman's Battle Beyond the Stars.

After blowing away the bad guys Sam tells Mike that they have orders to go solve a "problem" on Xarbia at a high security lab.  Subject 20 is an experiment   to create a new food source that has gone horribly awry.  Described as a meta morph, it has eaten a variety of test subjects (bunnies I guess) and cocooned itself in the lab.  Mike's suggestion to immediately kill it is strangely rejected by the team leader Dr. Hauser.  Later, a careless janitor cleaning up the carnage is eaten by an offspring of subject 20 while the janitor whirls around and around smashing into every glass object possible.   Meanwhile, Mike gets friendly with Dr. Barbara as Earl the security guy watches on close circuit TV.  Earl becomes aware of a security breach and goes out to investigate and gets eaten.   Tracy decides to take a steam bath while only wearing sunglasses, where Mike interrupts her because he was searching for the monster.  Mike decides to take a break and join her when the monster shows up.  The monster breaks through a skylight and goes out on to the planet surface.  Mike, SAM and two scientists go out after the monster.  They find Earl's body, but the monster has double backed to the lab where it kills Dr. Hauser.  While the boys think about how to kill the monster the girls go take a shower where they decide to peace out and attempt communication with the monster.

Dr. Barbara then learns that she can communicate with the monster with a computer from the 80's.  When she keys in CAN WE COEXIST? The monster responds by.... impaling her!

The monster then gets Brian while he is trying to radio for help.  With only Mike, Tracy and Dr. Cal left, Dr. Cal (who has cancer because he is always smoking) tells Mike to cut a cancerous tumor out of his body and feed it to the monster.  Mike is unsure of how to do it but Dr. Cal says he will talk him through it so Mike performs a gory surgery.  The monster breaks in just as Mike has cut out the tumor.  SAM sacrifices himself so Mike can slam dunk it into the monster’s mouth.  The monster then dies a disgusting death.

Thanks Don P!