Mismeasured Covariate in the Long-Term Survival of Colorectal Cancer

Mehdi Azizmohammad Looha,Soheila Khodakarim,Seyyed Vahid Hosseini,Mohamad Amin Pourhoseingholi

doi:10.31661/gmj.v8i0.1413

Abstract

Background: Colorectal cancer (CRC) is one of the most important causes of morbidity and mortality worldwide. This study aimed to determine the effect of measurement error of risk factors on the cure fraction of CRC patients. Materials and Methods: This study was conducted using the medical records of 346 patients with CRC, who were followed up between 2006 and 2017 in Shiraz, Iran. In our data, lymph node ratio (LNR) was a characteristic measuring with error. This variable was used in the model with 0.04 and 0.8 of error variance. Nonmixture nonparametric cure rate model and its corrected forms, simulation-extrapolation (SIMEX) and corrected score (CS), were applied to the data. Results: In noncured cases, the mean survival time was 1115.45 (95% confidence interval, 1043.60-1187.30) days. The 1-, 3-, and 5-year survival rates were 0.93, 0.71, and 0.65, respectively. The proportion of cured patients was 65.2%. The SIMEX method did not change the effect of LNR substantially on cure fraction as compared with the naive method when the variance of measurement error was 0.04 and 0.80. The CS method changed the effect of LNR on cure fraction even when the variance of measurement error was 0.04. Conclusion: The best method to assess the effect of LNR on cure fraction was the naive method, and the CS method was not deemed to be a valid method to correct the measurement error in LNR. [GMJ.2019;8:e1413]

Highlights

Colorectal cancer (CRC) is considered as the third and second most commonly diagnosed malignancy in men and women, respectively
In measuring patients’ characteristics, usually, there is no information about the distribution and variance of measurement error in the lymph node ratio (LNR); in SIMEX approach, we can use normal distribution for measurement error, which is robust to other distributions [19]
The 1, 3, and 5-year survival rates were 0.93, 0.71, and 0.65, respectively

Summary

Introduction

Colorectal cancer (CRC) is considered as the third and second most commonly diagnosed malignancy in men and women, respectively. If the follow-up time is sufficiently long, all subjects will eventually experience the event of interest; the population survival function will tend toward zero at infinity, whereas other common status in the analysis of time-to-event data occurs when subjects would never experience the event of interest These patients are termed as longterm survivors, immune, or cured. For such data, the survival curve has a stable plateau at the end of the study; we cannot use the classical survival model. The estimation of the cure fraction in cancer research is very important in providing information to patients and monitoring survival trend over time [18]. This study aimed to determine the effect of measurement error of risk factors on the cure fraction of CRC patients. Conclusion: The best method to assess the effect of LNR on cure fraction was the naive method, and the CS method was not deemed to be a valid method to correct the measurement error in LNR. [GMJ.2019;8:e1413] DOI:10.22086/gmj.v8i0.1413

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