First case report of fibropapillomatosis tumor regression identified through photoidentification and histopathology in a in Itapirubá, Santa Catarina, Brazil.

Background: Fibropapillomatosis (FP) is a tumor disease primarily affecting juvenile sea turtles, often characterized by external growths that can regress spontaneously. This study reports the first documented case of total tumor regression in a free-living green turtle () with FP in southern Brazil.

Case Description: A juvenile green sea turtle () was captured and recaptured on Itapirubá Beach, Santa Catarina, Brazil, showing signs of tumor regression with a period of 302 days between captures. At the first capture, photographs of the head and other regions were taken for photoidentification, along with documentation of fibropapilloma sites and tumor scoring. Tumor samples from the initial capture were histopathologically confirmed as fibropapillomas. At the recapture, the turtle showed a slight increase in carapace length, remaining classified as a juvenile. Tumors observed during the first capture were absent at recapture, with only scars remaining in the affected areas. Photoidentification confirmed the recapture, facilitating case monitoring. Tumor regression in this turtle is likely linked to various environmental and ecological factors.

Conclusion: Spontaneous regression of FP tumors remains a crucial indicator in the health monitoring of sea turtle populations. This is the first documented case of FP regression in this region of Brazil, suggesting that the turtle's increasing age and reduced exposure to anthropogenic pressure may have contributed to the tumor's regression. Although clinical follow-up of free-living sea turtles is challenging, reports of FP tumor regression are vital for understanding the health dynamics of sea turtle populations.