BACKGROUND: Implementation of a case surveillance study to detect antecedent exposures in a rare cancer requires sufficient case identification and accurate exposure ascertainment. We describe our approach for conducting a surveillance study for a cancer that occurs at a rate of approximately 3–5 per million per year and factors related to complete ascertainment of exposure.
OBJECTIVES: The primary objective of this study is to identify and interview at least 40% of diagnosed cases of osteosarcoma each year in US adults aged 40 years and older to ascertain antecedent exposures, including teriparatide, a product administered daily by self-injection for osteoporosis.
METHODS: Incident cases of histologically confirmed adult osteosarcoma diagnosed on or after January 1, 2003 are identified through cancer registries. Patients or their proxies are interviewed by telephone for osteosarcoma risk factors and selected exposures. Cases can only be interviewed if all central and local requirements for consent (which can vary greatly) are met. To evaluate factors related to interview rate, we examined the percent interviewed among total eligible to be interviewed by time from diagnosis to time patient was eligible for telephone contact as well as vital status at time of registry reporting.
RESULTS: The 14 participating registries historically capture approximately half of all adult US adult osteosarcoma cases. Between June 2004 and December 2006, 430 cases were identified; 303 cases diagnosed in 2003–2005 were eligible for telephone contact;123 of these cases were interviewed. There were no differences in demographic characteristics between patients interviewed and patients not interviewed. The interview rate for cases who were eligible for telephone contact in <12 months, 12–24 months or >24 months was 58%, 38% and 34% respectively. The interview rate by vital status at time of registry reporting was 48% if alive and 26% if deceased.
CONCLUSIONS: Targeted enrollment of a subset of state cancer registries and comprehensive cancer center registries allows us to identify more than half of US adult osteosarcoma cases. Shorter time between diagnosis and ability to contact patients is associated with a substantially higher interview success rate.
