Abstract
After undergoing liver transplantation, children are susceptible to oral lesions due to immunosuppressant drugs that are needed to maintain the transplant. In this context, it is important to understand how disease characteristics and age at transplantation influence the development of these lesions. Monitoring of lesions begins after transplantation and children are usually observed by a specialist in stomatology at periodic visits. Consequently, lesion development is estimated to occur between two observed times, and this is characterized as interval-censored data. However, in clinical practice, it is common to assume the moment of observation as the time of event occurrence, thereby excluding interval-censored data. Here, we discuss the impact of excluding interval-censored mechanisms in statistical analyses by using simulation studies to consider differences in sample sizes and amplitudes between observed intervals. Then, application studies are presented which use a data set from a prospective study that was conducted to investigate oral lesions in patients after liver transplantation at the A.C.Camargo Cancer Center in Brazil between 2013 and 2016 and a data set involving recurrent ovarian cancer in patients diagnosed with high-grade serous carcinoma at the A.C.Camargo Cancer Center between 2003 and 2016.
Highlights
After children undergo a liver transplant, they are susceptible to oral lesions due to the very strong dose of immunosuppression medicines that are needed to maintain the transplant
Stomatologists monitor children for lesions following surgery and they are interested in the influence of disease characteristics and age at transplantation on the time until lesions diagnosis, which is established as the period between the date of transplantions
*Correspondence: vinicius.calsavara@accamargo.org.br 3Department of Epidemiology and Statistics, A.C.Camargo Cancer Center, Rua Taguá, 440, Liberdade, 01509-010 São Paulo, Brazil Full list of author information is available at the end of the article to investigate the effect of several variables on a specified event occurrence. Both oral care and oral exams are performed by stomatology specialists at routine appointments following transplantation
Summary
After children undergo a liver transplant, they are susceptible to oral lesions due to the very strong dose of immunosuppression medicines that are needed to maintain the transplant. Researchers and analysts tend to apply traditional survival methodologies because they are easier and well-known, or because not all statistical softwares have procedures for analyzing interval-censored data Another important example of an interval-censoring mechanism involves time to recurrence in cancer. The Kaplan-Meier estimate is the simplest method for computing survival over time It is only adequate for right-censored data (i.e., the event occurs after the last follow-up). In a simulation study three data structures are assumed: i) interval-censored data (the original mechanism); ii) substituting the unobservable failure time with the observed event moment; and iii) substituting the unobservable failure time with the midpoint of the interval during which the event occurred These three approaches are applied to cases of oral lesion development in patients after liver transplantation and the practical relevance of ignoring interval-censored data is discussed. The following four sections include: a presentation of basic concepts of survival analysis, KaplanMeier estimator and Turnbull’s algorithm (“Background” section), a simulation study with different scenarios to numerically evaluate the impact of ignoring an intervalcensoring mechanism for obtaining survival function estimates (“Simulation study” section), two applications of real data sets are presented in “Applications” section, and final considerations are presented in “Final remarks” section
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