What drives tumor growth? Is it a few rogue cells imposing their will upon healthy tissue, or diseased tissue bringing out the worst in otherwise peaceable cells? Or is it a back-and-forth, a dialogue between the two? According to a new study, it may be the latter, at least when it comes to the progression of one common skin cancer.
Researchers found that a single mutated gene in an otherwise healthy stem cell can kick off an increasingly deviant feedback loop of miscommunication between the cancerous stem cell and its surrounding tissue, fueling the development of a malignant tumor. The findings suggest that many of the mutations in cancer may simply be setting in stone a path already forged by the tumor stem cell’s aberrant dialogue with its surroundings. If these results, published in Nature, prove broadly applicable, the findings could pave the way for novel approaches to treating a range of cancers.
“It’s not just that cancer molds the microenvironment, or that the environment affects the tumor,” says first author Shaopeng Yuan, a graduate student in the laboratory of Elaine Fuchs at The Rockefeller University. “Our study shows that there is crosstalk between the microenvironment and the stem cells in tumors. They communicate with each other and create a loop of tumor-promoting factors.”
Spotlight on squamous cell carcinoma
At the heart of almost every tumor is a small subset of cancer stem cells. Resistant to chemotherapy and immunotherapy, these malignant seeds are the cells responsible for keeping the tumor alive and are key players in the process that turns benign growths into metastatic disease. And behind many cancer stem cells, including those of skin, pancreatic, lung, and colorectal cancers, is a RAS gene that, when mutated, allows tissue stem cells to ignore normal environmental signals and deviate from their natural course, promoting out-of-control tissue growth.
To better understand the finer points of that interaction, Yuan and colleagues turned their attention to squamous cell carcinoma, a skin cancer linked to RAS mutations. The team started off by inducing mutant HRAS (the member of the RAS family most common in skin cancers) in individual skin stem cells, and monitoring how the cancerous stem cells interacted with the surrounding tissue. “Over time, the dialogue between the cancer stem cell and its microenvironment became more and more aberrant,” Fuchs says. “As we deciphered the dialogue, we realized that the miscommunication between the stem cell and its microenvironment resulted in the activation of much the same pathway that is active in the corresponding human cancers that harbor a high mutational burden.”
This observation raised an intriguing possibility. Perhaps many cancer mutations do not set the course of a disease so much as lock it in place, affirming a malignant progression already determined by aberrant crosstalk between a cancer stem cell and its microenvironment.
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