NEW YORK (CBSNewYork)– The location of cancer in colon cancer patients may predict the chance of survival, new research suggests.

After being diagnosed with advanced colon cancer, Marine combat veteran Tim Carroll says he was planning his funeral. Doctors told him with chemotherapy he had maybe two years to live.

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“Dealing with this kind of fight, you can’t shoot it or stab it or run it over,” Carroll told CBS2’s Dr. Max Gomez.

The 63-year-old’s tumor originated on the left side. A new study finds that metastatic colon cancer patients like Carroll survive significantly longer than patients with cancer that starts on the right side.

“People who had left-sided tumors actually had a much better prognosis than those that had a right-sided tumor. Actually greater than a year difference in their median survival,” said Dr. Jeffrey Meyerhardt of the Dana-Farber Cancer Institute.

Meyerhardt said the findings will likely change the way doctors approach both colorectal cancer treatment and future research.

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“Do the tumors that develop on the right side have different molecular features which lead to worse prognosis? Is it caught later? Because there are certain symptoms that you develop with a left-side tumor that may cause people to seek medical care sooner,” Meyerhardt said.

Analysis of over 1,000 colorectal cancer patients also found that the chemo drug Erbitux was more effective against left-sided tumors, while Avastin was better against right-sided cancer.

Carroll has survived for more than seven years. He’s had many surgeries and years of chemotherapy and said he will keep fighting.

“I guess I’m a lucky guy. I have a lot to live for. I have been through a lot,” he said.

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Molecular analysis of the different tumors should explain why there’s a survival difference, but until then doctors should treat right and left-sided tumors differently. The research will be presented at the annual meeting of the American Society of Clinical Oncology.