Michael Torres was 500 pounds and couldn't even raise his arm to run his fingers through his hair.

The South Florida resident said he had no desire to drop pounds, but that all changed when his twin sister, Ana Marin, was diagnosed with a rare cancer and needed him to save his own life in order to save hers.

Torres, 53, recently underwent gastric bypass surgery at South Miami Hospital, in order to be healthy enough to let doctors harvest his stem cells to give to his twin.

"The operation we did on him is a risky operation," said Dr. Jorge Rabaza. "But he took that risk not only to help himself, but to help his sister."

Marin was diagnosed with a rare form of lymphoma in 2008. For a year, she was able to fight off peripheral t-cell lymphoma by using her own stem cells, but doctors said they needed to start looking for a donor.

No one in her family tested positive for a match except her twin brother, but doctors said that performing surgery on someone so overweight posed too many risks. The procedure would be too painful and could put too much pressure on his heart.

So Torres decided he needed to lose the weight, and quickly.

Just over a decade ago, Torres weighed about 150 pounds and was very athletic, his family said. but after an accident left him bed ridden, Torres ballooned to 330 pounds in just a year and a half.

He tipped the scales at 500 pounds when doctors discovered his sister's cancer. Now Torres is 443 pounds.

He is expected to lose 100 pounds in three short months before he will be healthy enough for doctors to harvest his stem cells to transplant to his sister. But the weight-loss surgery has already transformed Torres' life.

"I wasn't able to touch my hair. I couldn't close my hands," Torres said Monday. "I washed my own hair today. Here I am and I'm doing fine. I'm a little uncomfortable, a little bloated."

Cancer experts can't say how successful the transplants will be because this type of lymphoma is extremely rare, but Torres and Marin are willing to give it their best shot.

The twins said they are complete opposites and fought all the time as children. Torres is left handed, Marin is right.

Torres loves eating fish and cheese, while his sister can't stand the taste of either.

Marin said she is grateful to have a twin who was willing to not only save her life, but also improve his own health.

"It's been so hard for the family for us," she said. "I had to take my brother's health into consideration because he's got to go through a lot of things. I can't just consider my health. This is my beautiful brother. I have to look after him."

After calling many surgeons to perform the operation on Torres, Rabaza was the only one that could be convinced to help the siblings.

Torres credits Rabaza, saying the doctor "stepped up to the plate and said, 'I'm going to get this done for you', and now he's not only saving my life, but the life of my sister."

Torres said it wasn't until now that he realized his purpose in life.

"God put me here on this earth for this day: to harvest my cells to save my sister," he said.