Researchers compared colorectal tumors from 189 patients ranging from age 29 to over 90 and found key differences that may explain why the cancer is more aggressive in younger people. The study, published October 29 in Nature Medicine, analyzed 54 tumors from patients under 50 and 135 from patients over 50.
Younger patients had a higher proportion of connective tissue cells relative to malignant cancer cells in their tumors, a pattern reversed in older patients. These connective tissue cells can secrete compounds that suppress the immune system and physically block chemotherapy drugs from reaching cancer cells, potentially explaining treatment resistance, according to Ana Anderson, a professor of neurology at Harvard Medical School and study co-author.
The researchers also found gene activity patterns in younger patients' tumors linked to cell-to-cell communication that may help cancer cells migrate through the body more easily. In other cancers, this type of gene activity has been associated with more aggressive tumors and greater likelihood of metastasis, Anderson said.
The analysis also revealed high levels of long noncoding RNA in younger patients' tumors. These RNA strands contain more than 200 building blocks but do not provide instructions for building proteins. Scientists do not yet understand what these strands do in tumors. Anderson and her team are beginning to manipulate the RNA they found in cancer cells in laboratory dishes to investigate further.
Colorectal cancer rates in people under 50 have been rising since the mid-1990s and now represent the leading cause of cancer death in that age group, according to the report.