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. 2014 Oct;16(10):1400-7.
doi: 10.1093/neuonc/nou053. Epub 2014 Apr 9.

Incidence and relative survival of anaplastic astrocytomas

Nicolas R Smoll  1 , Brett Hamilton  1
Affiliations

Incidence and relative survival of anaplastic astrocytomas

Nicolas R Smoll et al. Neuro Oncol. 2014 Oct.

Abstract

Background: The purpose of this study was to investigate the relationship between age and the incidence and relative survival of anaplastic astrocytoma (AA).

Methods: Data from the Surveillance, Epidemiology and End Results database were used to identify 3202 patients with AA. These data were analyzed to assess incidence rates, relative survival, and the standardized mortality ratio across age groups. Time trends were modeled using delayed-entry modeling.

Results: The overall incidence of AA was an age-adjusted rate of 3.5 per million person/years. The overall age-standardized 5- and 10-year relative survival rates of populations with AA were 23.6% and 15.1%, respectively. The overall standardized mortality ratio for the entire cohort was 46 (95% confidence interval: 45, 48).

Conclusions: Patients with a diagnosis of AA are 46 times more likely to die than persons matched for age/sex/year of the general population. The effect of age on survival is present for only the first 2 years postdiagnosis. Measuring the effect of age on survival for populations with an AA is not amenable to using models with proportional hazards as an assumption because of the presence of a reverse fork-type interaction.

Keywords: anaplastic astrocytoma; brain tumor; nonproportional hazards; relative survival; standardized mortality ratio.

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Figures

Fig. 1.
Fig. 1.
Smoothed incidence rates (per 1 million) across patient ages at diagnosis, by sex. The bottom graph is placed here to demonstrate that the differences between sexes is in fact small (irrespective of P-value).
Fig. 2.
Fig. 2.
Time trends of the incidence of AA (SEER 9) demonstrating stability in the later years.
Fig. 3.
Fig. 3.
(A) Overall survival and (B) RS curves as measured by the Kaplan–Meier method and RS methods. Relative survival cannot be calculated at time zero, which is why the first period is absent (SEER 18).
Fig. 4.
Fig. 4.
Longitudinal period RS rates of AAs by age group. Two-year longitudinal period RS EAPC: −0.13% (95% CI: −0.47, 0.22%; P = .46). Five-year longitudinal period RS EAPC: −0.13% (95% CI: −0.43, 0.17%; P = .39). Demonstrating a relatively stable trend, rather than any obvious up- or downtrends.
Fig. 5.
Fig. 5.
Longitudinal period RS rates of AAs by age group. Demonstrates that changes in 5-year survival rates have not had an obvious uptrend.
Fig. 6.
Fig. 6.
Post-estimation visual inspection of the piecewise constant hazards model. Observed (dots with capped spikes) and model predictions (dotted lines). Demonstrates an accurate model using the interaction term. Nest model (without interaction term) demonstrated a fit that was visually inaccurate, and the likelihood ratio test for model differences was P < .05 compared with the full model.
Fig. 7.
Fig. 7.
Line graph of eHRs of the piecewise constant hazards survival model. The lines that begin as separate and then converge later in follow-up demonstrate change in eHR over time. This is a visual representation of nonproportional hazards—more specifically, the reverse-fork interaction.
See this image and copyright information in PMC

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