Stephen Morrell ^1* David Roder ² David Currow ³ Alexander Engel ^4,5 Elizabeth Hovey ^6,7 Craig R. Lewis ^6,7 Winston Liauw ^7,8 Jarad Martin ^10,11,9 Manish Patel ^12,13 Stephen R. Thompson ^14,7 Tracey O'brien ¹

• ¹ Cancer Institute of New South Wales, Sydney, Australia
• ² Cancer Epidemiology and Population Health, University of South Australia, Adelaide, Australia
• ³ Faculty of Science, Medicine and Health, University of Wollongong, Wollongong, New South Wales, Australia
• ⁴ Northern Sydney Cancer Centre, Royal North Shore Hospital, St Leonards, New South Wales, Australia
• ⁵ Faculty of Medicine and Health, The University of Sydney, Sydney, New South Wales, Australia
• ⁶ Department of Medical Oncology, Prince of Wales Hospital, University of New South Wales, Randwick, New South Wales, Australia
• ⁷ School of Clinical Medicine, Faculty of Medicine, University of New South Wales, Sydney, New South Wales, Australia
• ⁸ St George Hospital, Kogarah, New South Wales, Australia
• ⁹ School of Medicine and Public Health, University of Newcastle, Newcastle, Australia
• ¹⁰ Department of Radiation Oncology, Calvary Mater Newcastle Hospital, Newcastle, New South Wales, Australia
• ¹¹ GenesisCare Maitland, Maitland, Australia
• ¹² Western Clinical School, Faculty of Medicine and Health, The University of Sydney, Sydney, New South Wales, Australia
• ¹³ Faculty of Medicine, Health and Human Sciences, Macquarie University, Sydney, New South Wales, Australia
• ¹⁴ Nelune Comprehensive Cancer Centre, Prince of Wales Hospital, University of New South Wales, Randwick, New South Wales, Australia

Population cancer registries record primary cancer incidence, mortality and survival for whole populations, but not more timely outcomes such as cancer recurrence, secondary cancers or other complications that disrupt event-free survival. Nonetheless, indirect evidence may be inferred from treatment data to provide evidence of recurrence and like events, which can facilitate earlier assessment of care outcomes.The present study aims to infer such evidence by applying algorithms to linked cancer registry and treatment data obtained from hospitals and universal health insurance claims applicable to the New South Wales (NSW) population of Australia.Primary invasive cancers from the NSW Cancer Registry (NSWCR), diagnosed in 2001-2018 with localized or regionalized summary stage, were linked to treatment data for five common Australian cancers: breast, colon/rectum, lung, prostate, and skin (melanomas). Clinicians specializing in each cancer type provided guidance on expected treatment pathways and departures to indicate remission and subsequent recurrence or other disruptive events.A sample survey of patients and clinicians served to test initial population-wide results. Following consequent refinement of the algorithms, estimates of recurrence and like events were generated. Their plausibility was assessed by their correspondence with expected outcomes by tumour type and summary stage at diagnosis and by their associations with cancer survival.Kaplan-Meier product limit estimates indicated that 5-year cumulative probabilities of recurrence and other disruptive events were lower, and median times to these events longer, for those staged as localized rather than regionalized. For localized and regionalized cancers respectively, these were: breast -7% (866 days) and 34% (570 days); colon/rectum -15% (732 days) and 25% (641 days); lung -46% (552 days) and 66% (404 days); melanoma -11% (893 days) and 38% (611 days); and prostate -14% (742 days) and 39% (478 days). Cases with markers for these events had poorer longer-term survival.These population-wide estimates of recurrence and like events are approximations only. Absent more direct measures, they nonetheless may inform service planning by indicating population or treatment sub-groups at increased risk of recurrence and like events sooner than waiting for deaths to occur.