In Reply We appreciate the interest of Chidambaram and Goh in our study, in which we demonstrate age, sex, and tumor size as important predictors of survival in patients with dermatofibrosarcoma protuberans (DFSP).1
We emphasize again the objective of our study was to examine prognostic factors on a large scale for an exquisitely rare tumor, the yearly incidence of which is estimated to be 0.8 to 4.5 cases per million in the United States.2 We acknowledge the limitations of the data available in the Surveillance, Epidemiology, and End Results (SEER) program, which, while robust, do not provide details of histologic tumor characteristics. While histologic confirmation is provided, the SEER data do not detail specific features such as fibrosarcomatous change or mitoses. There is a paucity of studies providing prognostic factors for DFSP in the literature, likely owing to the rarity of the disease. SEER compiles cancer data from 18 population-based cancer registries encompassing approximately 30% of the US population.3 It provides the only statistically viable means by which to examine prognostic factors at all. Data from SEER is publicly available and purposely stripped of identifiable patient information, making linkage to specific pathology reports impossible. In addition, staging guidelines for DFSP do not consistently account for specific histologic features, making reporting of such features variable. Tumor size and anatomic location in DFSP, however, are recognized as 2 factors that dictate treatment modality, both of which we controlled for in our multivariable analyses. Furthermore, our study goes beyond the clinical data available in SEER through its linkage with the American Community Survey to adjust for demographic variables.
Criscito MC, Martires KJ, Stein JA. Prognostic Factors of Survival in Dermatofibrosarcoma Protuberans—Reply. JAMA Dermatol. 2016;152(12):1398-1399. doi:10.1001/jamadermatol.2016.3226