The Many Faces of Melanoma
We’ve heard the story before: a woman is treated successfully for her melanoma, only to have the cancer come back after ten years. How? Why? One explanation is something called “tumor heterogeneity.”
“Tumor heterogeneity” means a tumor may have many different types of cells within it. Cancer cells are normal cells that have mutated, and they are remarkably good at mutating. These changes don’t stop with the onset of cancer or with the beginning of treatment. I’ve heard a researcher compare a tumor cell to a tree: at the beginning it is united, like the trunk, but then it begins to branch out. Each branch is different and gives birth to other branches that are different still.
This variation among cells causes problems. Advances in pathology mean that smaller tissue samples are being used to conduct key tests. What if that sample contains only one form of the tumor and not others? It means doctors could miss important characteristics of the tumor by looking at too small a sample.
Tumor heterogeneity also explains why cancers seem to develop resistance to treatment. Perhaps most of the tumor cells share a common characteristic that makes them susceptible to a therapy. They are killed off, but the small percentage of cells that have mutated are able to withstand the treatment. The cancer in those cells has not become resistant. Rather, a very small percentage of the cancer cells were resistant all along. When treatment kills the other cells, that minority form can flourish unchecked.
This means tumors need to be analyzed more thoroughly. Instead of looking for a single mutation that may exist in some tumor cells and treating for that mutation, we need to look for the mutations that are common across the entire tumor.
More importantly, this shows that treating cancer is not often a single treatment approach. Combination therapies, such as those being conducted by the MRF’s Breakthrough Consortium (MRFBC), are critically important. They have the best chance of killing all the different variations of the tumor. Further, a treatment schedule is likely to involve using, over time, a number of different therapies until the tumor is finally exhausted and the cancer is gone.
Our understanding of cancer continues to expand rapidly and the treatment options for melanoma are expanding rapidly. Keep up to date with the MRFBC and the MRF’s research funding here: http://www.melanoma.org/research/melanoma-research.