Comparative survival analysis of melanoma patients with secondary papillary thyroid carcinoma using Surveillance, Epidemiology, and End Results (SEER) data

Abstract

9068 Background: Malignant melanoma (MM) and papillary thyroid cancer (PTC) may share genetic mutations. The expected mortality of a patient with both MM and PTC should be predominantly influenced by MM and unchanged by the PTC diagnosis, unless shared genetic abnormalities or other factors alter the phenotype of either or both diseases. We hypothesize patients with both MM and PTC have altered mortality risk compared to patients with either cancer alone. Methods: The study population included patients identified in the SEER 1973–2004 database who were diagnosed with MM or PTC as a primary tumor. The population was divided into four groups: (1) patients with MM only (MEL); (2) patients with PTC only (PAP); (3) patients who developed MM as a second primary after PTC (2MEL); and (4) patients diagnosed with PTC after MM (2PAP). Time between diagnosis and death or last follow up (December 2005) and other demographic data was obtained from SEER. Comparisons between the group death rates were made using the Chi-Square Test. A Cox proportional hazards regression model, adjusted for patient characteristics, predicted the risk of death and survival by group. Results: 9575 SEER patient records were included: 6622 in MEL, 2778 in PAP, 113 in 2MEL and 62 in 2PAP. Overall, 2095 patients (22%) died. There was a significant difference in mortality rates between the groups: MEL 27%, PAP 9%, 2MEL 21% and 2PAP 18%, p<0.001 by Chi-Square. Controlling for other variables in a multivariate Cox model, patients in the 2MEL group were significantly less likely to die than MEL patients (HR 0.52, 95% CI 0.35–0.79, p=0.002). 2PAP patients, the smallest sample, also had a reduced likelihood of death that did not reach statistical significance (HR=0.75, 95% CI 0.42–1.37, p=.35). PAP patients had the best survival (HR=0.43, 95% CI 0.36–0.50,p<0.001). Other factors (age, race, gender and radiation therapy, data not shown) also significantly affected mortality. Conclusions: This study suggests that MM patients also diagnosed with PTC are more likely to survive than patients with MM alone. Identification of the causative factor(s) for this survival benefit will require additional epidemiologic and genetic studies. No significant financial relationships to disclose.