Background: The prognoses widely reported for pancreatic cancer reflect the very poor survival associated with the most common histological type, exocrine adenocarcinoma. We calculated life expectancies for patients with less common pancreatic neuroendocrine tumors (PNETs), and also for the subsets of these patients who survive 1 and 5 years post-diagnosis, all of which carry a significantly better prognosis. Results for 1- and 5-year PNET survivors appear not to have been previously reported, nor have life expectancies (average long-term survival times) been given.
Methods: We identified 5287 cases of PNET in the SEER US national database, 1973-2013. The Kaplan-Meier estimator was used to compute empirical survival probabilities and median survival times for functioning (n = 279) and non-functioning PNET (n = 5008) cases. The Cox proportional hazards regression model was used to examine univariate associations of survival with covariates including patient age, sex, race, cancer stage, tumor grade, surgical treatment, and calendar year. A multivariate multiplicative hazard Poisson regression model estimated mortality rates for all combinations of the covariates. The rates were used to construct actuarial life tables, which gave life expectancies for male and female patients according to age, cancer stage, tumor grade, histology (functioning versus non-functioning), surgical treatment status, and time since diagnosis. These life expectancies were compared with age- and sex-specific figures from the US general population.
Results: Life expectancy in PNET is lower than that of the US general population and varies significantly according to patient age, cancer stage, tumor grade, mode of treatment, and time since diagnosis. For example, it is near normal for persons aged 70 and older who undergo surgical resection of localized well-differentiated (i.e., grade I) tumors. By contrast, persons with metastatic high-grade tumors not amenable to surgery have life expectancies of only 1 to 4 years depending on patient age. Functioning PNETs were associated with somewhat lower mortality than non-functioning within the first few years after diagnosis, though no major differences were observed long-term. Positive factors for survival were younger age, localized stage, low tumor grade, and surgical treatment. Survival improved over the 1973-2013 study period: on average mortality rates fell by 1.2% per year after controlling for changes in the patient population. Life expectancy increased markedly with time since diagnosis: those surviving 1 and 5 years post-diagnosis had longer additional life expectancies.
Conclusions: Life expectancies of patients with PNETs may be markedly reduced from normal, but even in the worst cases their prognoses remain significantly better than that of patients with the more common pancreatic adenocarcinomas. In some very favorable cases, the life expectancy is near-normal, especially amongst 1- and 5-year survivors. This information can be used to counsel patients.
Keywords: Conditional survival; Epidemiology; Malignant; PNET; SEER; Survival.
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