Cancers are diverse, and that makes them extremely difficult to treat. What worked stunningly for one person might fail utterly for another. What worked for a tumor in the brain probably won't work on a cancer of the liver. Scientists are trying to outwit tumors by coming up with tailored treatments like the immunotherapy drug used to successfully treat former President Jimmy Carter.
But it's very hard to figure out how to find the right drug for a specific patient. A paper published Friday in Nature Communications suggests one thing that might help is identifying the astonishing mix of cells inside a tumor. It's not just cancer in there.
Tumors can swallow up cells around them and grow into composites of malignant and healthy tissue. As that happens, they seem to take on different properties that could make them more or less responsive to an immunotherapy drug like Pembrolizumab, the medication that Carter received, one that works by stimulating the immune system to attack tumors, researchers say.
A lot of that has to do with the kinds of cells the tumor has taken up as it grows. "Cancers actually have a lot of different types of cells in them, including immune cells or inflammatory cells that contribute to the impurity of the cancer in terms of pure cancer cells," says Dr. Atul Butte, the director for the Institute for Computational Health Sciences at the University of California, San Francisco, who authored the study in Nature Communications on treating cancer with immunotherapy drugs.
By analyzing a database of tens of thousands of cancer patients in an open-access tool called the Cancer Genome Atlas, Butte and his colleagues saw that the composition of a tumor correlated with the success of treatment. "The purity of their cancer actually had a lot to do with whether or not that patient ended up surviving that cancer and whether a particular drug seemed to be effective or not," Butte says.
One of the most important types of cells embedded in tumors is immune cells, according to Dr. Reena Thomas, a neuro-oncologist at Stanford Health Care who was not involved in the study. Some tumors, like the melanoma that Carter was treated for, have more immune cells than others or are in more immune-sensitive locations like the brain.
That might make immunotherapy drugs more potent, since immune cells have already infiltrated the tumor itself or are concentrated nearby. "Then things like immune therapy might be more prone to working because if you activate those cells, they're able to actually get in and have an anti-tumor effect," Thomas says. But if a tumor spreads to a different part of the body, like the lungs or the liver, the immune properties of that tumor might change.
The study found that some tumors carried an immune therapy gene signature that other tumors didn't, Thomas says. "That gives us a clue as to knowing why some patients like President Carter might respond to this therapy, but it could be by cancer and it could be by patient."
The only way to know for sure is to actually sample every tumor in every spot, Butte says. That would help oncologists figure out what the composition of a tumor means in the context of different drugs. "More detailed measurements of cancers, biology and DNA are increasingly important for us to reach this precision medicine targeting the right drugs," he says. "We need better tools and models, but the data and the measurements are going to get us there."
Immunotherapy, like chemotherapy, is extremely expensive and can make people seriously ill. "Why subject a patient to something like that, if one of those patients is made to be one of the responders for immune therapy in the first place?" Thomas says.
It will take a lot more data before truly targeted, personalized treatments are available for everyone. But Thomas and Butte both hope that eventually research will get to a point where we can create a treatment plan for every cancer scenario. "If we can harness a particular chemotherapy plan to be specific to a [patient's] tumor type and genetic signature, that the best thing we can do for them," Thomas says.