Temporal trends in competing mortality from second and subsequent primary cancers, 1980-2014: An Australian population-based study.

BACKGROUND: Subsequent primary cancers (SPCs) compete with first cancers and non-cancer events as the primary cause of death among cancer patients. We aimed to assess temporal trends in SPC mortality since 1980 among adult-onset cancer patients in competing risk models. METHODS: Patients registered with a first cancer in the population-based Tasmanian Cancer Registry, Australia, between 1980-2009 were followed up to December 2014. Cumulative incidence function (CIF) was used to estimate the cumulative incidence of cause-specific deaths in the presence of competing risks. The hazard ratios of SPC-specific deaths were assessed in two regression models: subdistribution hazard ratios from competing risk models (SHRs) and hazard ratios from Cox models (CHRs). RESULTS: Overall, 5339 (9.3%) of 57,288 patients developed SPCs and 2494 died from SPCs during the follow-up. While the cumulative incidence of first cancer deaths at 5, 10, 15 and 20-years gradually decreased over periods of first cancer diagnosis, the cumulative incidence of SPC deaths did not. The SHRs for SPC-specific deaths increased from the reference period 1980-1984 to a peak for first cancers diagnosed in 1995-1999 (SHR = 1.18, 95%CI 1.03-1.35), before a decrease in 2005-2009 (SHR = 0.82, 95%CI 0.70-0.95) in competing risk models. However, this pattern was not consistent in CHRs. For individuals with specific first cancers, those with a first prostate cancer in 1995-1999 ha d the greatest SPC mortality risk (SHR = 2.08, 95%CI 1.29-3.36). CONCLUSION: Competing risk models, but not Cox models, demonstrated temporal increases in SPC-specific mortality. Greater detection of non-fatal first prostate cancers appears to have contributed to this trend.

Effects of the length of central cancer registry operations on identification of subsequent cancers and on survival estimates.

BACKGROUND: Population-based cancer survival analyses have traditionally been based on the first primary cancer. Recent studies have brought this practice into question, arguing that varying registry reference dates affect the ability to identify earlier cancers, resulting in selection bias. We used a theoretical approach to evaluate the extent to which the length of registry operations affects the classification of first versus subsequent cancers and consequently survival estimates. METHODS: Sequence number central was used to classify tumors from the New York State Cancer Registry, diagnosed 2001-2010, as either first primaries (value=0 or 1) or subsequent primaries (≥2). A set of three sequence numbers, each based on an assumed reference year (1976, 1986 or 1996), was assigned to each tumor. Percent of subsequent cancers was evaluated by reference year, cancer site and age. 5-year relative survival estimates were compared under four different selection scenarios. RESULTS: The percent of cancer cases classified as subsequent primaries was 15.3%, 14.3% and 11.2% for reference years 1976, 1986 and 1996, respectively; and varied by cancer site and age. When only the first primary was included, shorter registry operation time was associated with slightly lower 5-year survival estimates. When all primary cancers were included, survival estimates decreased, with the largest decreases seen for the earliest reference year. CONCLUSIONS: Registry operation length affected the identification of subsequent cancers, but the overall effect of this misclassification on survival estimates was small. Survival estimates based on all primary cancers were slightly lower, but might be more comparable across registries.