Green Turtle Fibropapillomatosis: Tumor Morphology and Growth Rate in a Rehabilitation Setting

Simple Summary Green turtles (Chelonia mydas) are globally afflicted by a tumoral disease called fibropapillomatosis (FP). Affected turtles experience growth of tumors on various parts of their body, including skin tissue on the flippers and neck as well as in the eyes and mouth. Internal tumors also occur sometimes, for example, on heart, lungs, and kidneys. Since FP was first described in 1938, FP tumors have been categorized into two main morphological types: rugose and smooth tumors. Rugose tumors are characterized by papillose structures and a rough texture, while smooth tumors have a smoother and more even surface and texture. It has often been suggested in the literature that, while rugose tumors tend to show active growth, smooth tumors might be a sign of disease regression. However, this hypothesis warrants further verification. In our study, we tracked and compared the growth of rugose and smooth tumors across nine green turtles in rehabilitation at the University of Florida Whitney Laboratory Sea Turtle Hospital in St. Augustine, Florida. According to our findings, rugose FP tumors grow at significantly faster rates than smooth ones, but both FP tumor morphologies still show a general progression pattern. Our study is, to our knowledge, the first-ever assessment of growth-rate differences between smooth and rugose FP tumors and offers important preliminary data to answer a long-standing question in FP research. Abstract Fibropapillomatosis (FP) is a neoplastic disease most often found in green turtles (Chelonia mydas). Afflicted turtles are burdened with potentially debilitating tumors concentrated externally on the soft tissues, plastron, and eyes and internally on the lungs, kidneys, and the heart. Clinical signs occur at various levels, ranging from mild disease to severe debilitation. Tumors can both progress and regress in affected turtles, with outcomes ranging from death due to the disease to complete regression. Since its official description in the scientific literature in 1938, tumor growth rates have been rarely documented. In addition, FP tumors come in two very different morphologies; yet, to our knowledge, there have been no quantified differences in growth rates between tumor types. FP tumors are often rugose in texture, with a polypoid to papillomatous morphology, and may or may not be pedunculated. In other cases, tumors are smooth, with a skin-like surface texture and little to no papillose structures. In our study, we assessed growth-rate differences between rugose and smooth tumor morphologies in a rehabilitation setting. We measured average biweekly tumor growth over time in green turtles undergoing rehabilitation at the University of Florida Whitney Laboratory Sea Turtle Hospital in St. Augustine, Florida, and compared growth between rugose and smooth tumors. Our results demonstrate that both rugose and smooth tumors follow a similar active growth progression pattern, but rugose tumors grew at significantly faster rates (p = 0.013) than smooth ones. We also documented regression across several examined tumors, ranging from −0.19% up to −10.8% average biweekly negative growth. Our study offers a first-ever assessment of differential growth between tumor morphologies and an additional diagnostic feature that may lead to a more comprehensive understanding and treatment of the disease. We support the importance of tumor morphological categorization (rugose versus smooth) being documented in future FP hospital- and field-based health assessments.