Cure for a common turtle cancer takes a lesson from human cancers

A one-two punch can knock out a common cancer in sea turtles. Just as some human cancers are best treated first by surgical removal of the tumor and then by chemotherapy, surgery and treatment with the anticancer drug fluorouracil reduced the reoccurrence of the sometimes deadly turtle cancer fibropapilloma from 60% to 18%, researchers report today in Communications Biology .

The cancer often leads to rapidly growing tumors on the mouth, in the eyes, and on the flippers that interfere with eating, swimming, and other functions—at times so much that the animals ultimately die. Biologists in Florida first noticed the disease in green sea turtles (Chelonia mydas, pictured) more than a century ago and by the 1990s had learned it was spread by a herpeslike virus. Today, this cancer is found all over the world, particularly in warmer places.

When researchers working at a sea turtle hospital in Florida compared gene activity in tumors with gene activity in healthy green sea turtle tissue, they discovered that the tumors thrive thanks to a network of proteins that is very similar to the network of proteins that promote a human skin cancer, basal cell carcinoma. Hence, they tried anticancer drugs on the turtles.

The comparison showed that the virus itself is inactive once the tumor gets started and surprisingly, genes that control the formation of nerve cells are also very active in the cancerous tissue, they note.

Just as sunlight is a risk factor for this human skin cancer, sunlight seems to increase the chances for this the turtle disease, the researchers report. Other environmental factors, such as pollution, likely come into play as well, they note, as the tumors are rarely seen in animals living in pristine environments, even though those animals carry the virus.

The incidence of these tumors has increased 10-fold over the past decade, but the disease doesn’t seem to be making much of a dent in the green sea turtle’s recovery from near extinction. Thanks to regulations to reduce the number of turtles caught for food or trapped in fishing gear, their numbers have grown exponentially in recent years.