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Review
. 2016 Feb 11;55(2):134-41.
doi: 10.1515/sjph-2016-0012. eCollection 2016 Jun 1.

Cancer Patients' Survival: Standard Calculation Methods And Some Considerations Regarding Their Interpretation: POPULACIJSKO PREŽIVETJE BOLNIKOV Z RAKOM: UPORABA RAZLIČNIH PRISTOPOV IN PROBLEMI INTERPRETACIJE REZULTATOV

Vesna Zadnik  1 , Tina Žagar  1 , Maja Primic Žakelj  1
Affiliations
Review

Cancer Patients' Survival: Standard Calculation Methods And Some Considerations Regarding Their Interpretation: POPULACIJSKO PREŽIVETJE BOLNIKOV Z RAKOM: UPORABA RAZLIČNIH PRISTOPOV IN PROBLEMI INTERPRETACIJE REZULTATOV

Vesna Zadnik et al. Zdr Varst. .

Abstract
in English, Slovenian

Background: Cancer patients' survival is an extremely important but complex indicator for assessing regional or global inequalities in diagnosis practices and clinical management of cancer patients. The population-based cancer survival comparisons are available through international projects (i.e. CONCORD, EUROCARE, OECD Health Reports) and online systems (SEER, NORDCAN, SLORA). In our research we aimed to show that noticeable differences in cancer patients' survival may not always reflect the real inequalities in cancer care, but can also appear due to variations in the applied methodology for relative survival calculation.

Methods: Four different approaches for relative survival calculation (cohort, complete, period and hybrid) have been implemented on the data set of Slovenian breast cancer patients diagnosed between 2000 and 2009, and the differences in survival estimates have been quantified. The major cancer survival comparison studies have been reviewed according to the selected relative survival calculation approach.

Results: The gap between four survival curves widens with time; after ten years of follow up the difference increases to more than 10 percent points between the highest (hybrid) and the lowest (cohort) estimates. In population-based comparison studies, the choice of the calculation approach is not uniformed; we noticed a tendency of simply using the approach which yields numerically better survival estimates.

Conclusion: The population-based cancer relative survival, which is continually reported by recognised research groups, could not be compared directly as the methodology is different, and, consequently, final country scores differ. A uniform survival measure would be of great benefit in the cancer care surveillance.

Izhodišča: Preživetje bolnikov z rakom je kompleksen kazalnik, ki je izjemno pomemben pri ocenjevanju regijskih in globalnih neenakosti v diagnostiki in zdravljenju onkoloških bolnikov. Med najbolj prepoznavne mednarodne projekte, ki periodično objavljajo primerjave populacijskega preživetja bolnikov z rakom, sodijo CONCORD, EUROCARE in zdravstvena poročila OECD. Za nekatere populacije pa je populacijsko preživetje bolnikov z rakom na voljo tudi na spletnih aplikacijah, kot so SEER (Združene države Amerike), NORDCAN (Skandinavija) in SLORA (Slovenija). Z našo raziskavo smo želeli opozoriti, da nekatere očitne razlike med preživetjem onkoloških bolnikov iz različnih držav niso nujno posledica neenakosti v organizaciji, dostopnosti, kakovosti ali učinkovitosti sistema zdravstvenega varstva, temveč da lahko odstopanja nastanejo tudi le zaradi razlik v metodologiji, uporabljeni pri izračunavanju relativnega preživetja.

Metode: V analizi smo primerjali štiri metode za izračunavanje relativnega preživetja: kohortni, popolni, obdobni in mešani (hibridni) pristop. Razlike smo kvantificirali na primeru relativnega preživetja slovenskih bolnic, ki so zbolele za rakom dojke med letoma 2000 in 2009. V drugem delu raziskave smo naredili pregled izborov pristopov k izračunavanju relativnega preživetja v najpomembnejših mednarodnih raziskavah.

Rezultati: Razkorak med preživetvenimi krivuljami se veča s časom: deset let po diagnozi naraste razlika med najboljšo (hibridni pristop) in najslabšo (kohortni pristop) oceno že na 10 odstotnih točk. Ugotavljamo tudi, da pristop k izračunavanju relativnega preživetja med osrednjimi mednarodnimi projekti ni poenoten. Poleg tega se nakazuje tendenca po uporabi pristopov, pri katerih so ocene preživetja višje.

Zaključek: Populacijsko preživetje onkoloških bolnikov, ki ga v svojih publikacijah prikazujejo ugledne mednarodne raziskovalne skupine, ni neposredno primerljivo. Načini izračunavanja se namreč razlikujejo tako med raziskovalnimi skupinami kot tudi znotraj posamezne skupine. V zadnjih letih smo že bili priča interpretacijam razlik v relativnem preživetju bolnikov z rakom iz različnih držav, ki so bile pristranske prav zaradi neupoštevanja razlik, ki nastanejo pri uporabi različnih metod izračunavanja. Prepričani smo, da bi javnozdravstvena stroka in politika veliko pridobili s poenotenjem izračunavanja preživetja bolnikov z rakom.

Keywords: bias; cancer registries; cancer survival; populacijska analiza preživetja; population-based survival analysis; preživetje bolnikov z rakom; pristranskost; register raka; relative survival; relativno preživetje.

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Conflict of interest statement

The authors declare no conflicts of interest.

Figures

Figure 1
Figure 1
The illustration of the choice of patients diagnosed between the years 2000 and 2009 that contribute to a relative survival calculation with cohort, complete and period approaches (top: a follow up untill the end of 2010) and those that contribute to the hybrid approach (bottom: a follow up untill the end of 2012).
Figure 2
Figure 2
The relative survival curves derived by cohort, complete, period and hybrid approaches, and Kaplan-Meier observed survival for Slovenian female breast cancer patients diagnosed between 2000 and 2009.
See this image and copyright information in PMC

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