We obtained tumor and lung tissue from patients during surgical resection, and although surgically treated patients tend to be slightly younger and have more epithelioid disease compared to the total MPM patient population, this cohort is highly similar to other surgically treated cohorts (Pass et al. 2008
). Survival data were available on all 128 cases; of these, 83 cases had available asbestos body burden data. Among the cases with available AB counts, three had extremely high counts—14,870, 19,681, and 303,852 ABs per gram of wet weight lung (ABs/g lung)—compared to the median count of 158. To avoid an analysis anchored by extreme values, we did not include data from these three patients.
In , we present exposure, demographic, and tumor histology data for all 128 cases and for the subset of 80 cases with asbestos burden data. Cases with asbestos burden data did not differ significantly from cases without fiber burden data.
Demographics and tumor characteristics of mesothelioma patients.
“Survival time” was defined as the time from diagnosis to death or last known follow-up. shows the Kaplan-Meier survival probability plots stratified by sex, and the log-rank test indicates a significantly reduced survival for males compared to females (p < 0.04). Similarly, shows the Kaplan-Meier survival plots by tumor histology. These data reveal a significant difference in survival between patients with epithelioid and nonepithelioid histologies (log-rank p < 0.02), as well as a significant difference among epithelioid, biphasic, and sarcomatoid histologies (log-rank p < 0.01).
Figure 1 Kaplan-Meier survival probability plots of MPM patients (n = 128) by sex, using the log-rank method to test for a difference between strata. Males (n = 98) had significantly reduced survival compared to females (n = 30; p < 0.04). Surviving patients (more ...)
Figure 2 Kaplan-Meier survival probability plots of MPM patients (n = 128) based on tumor histology, using the log-rank method to test for a difference between strata. (A) Survival of patients with an epithelioid tumor (n = 91) and those with a mixed or sarcomatoid (more ...)
We then examined the relationships among asbestos exposure, asbestos fiber burden, patient demographics, tumor histology, and survival data, and we found a significant difference among asbestos fiber burden levels and survival. Among all 128 cases, self-reported exposure to asbestos was not predictive of survival in MPM (log-rank p = 0.44; data not shown). However, we observed a significant association between self-reported asbestos exposure and older age at diagnosis (reported exposure, 62.0 ± 9.5 years; no reported exposure, 56.9 ± 9.7 years; t-test, p < 0.05), as well as between male sex and reported asbestos exposure (Fisher’s, p < 0.0001; data not shown). Quantitative asbestos burden data from 80 cases showed that males (median count, 219 ABs/g lung; range, 0–6,211) had significantly higher asbestos burden than females (median count, 20 ABs/g lung; range, 0–2,437; Wilcoxon p < 0.0001). Models of survival by asbestos exposure did not demonstrate a linear trend; thus, data were stratified into tertiles for subsequent analysis. After stratifying asbestos burden data into tertiles of low burden (0–99 ABs/g lung), moderate burden (100–1,099 ABs/g lung), and high burden (> 1,099 ABs/g lung), we found an association of fiber burden with survival among these groups that approached statistical significance (; log-rank p = 0.06). Using a Cox proportional hazards model to adjust for covariates, cases with low asbestos fiber burden had a 3-fold elevated risk of death [95% confidence interval (CI), 0.95–9.5; p = 0.06] compared to cases with moderate burden (). Patients with high asbestos fiber burden had 4.8-fold elevated risk of death (95% CI, 1.5–15.0; p < 0.01) compared to patients with moderate burden (). Including the three cases with extreme outlying asbestos counts in this model did not significantly alter the results (data not shown).
Figure 3 Kaplan-Meier survival probability plots of MPM patients based on asbestos burden, using the log-rank method to test for a difference among strata. Survival differences among exposure groups approaches statistical significance (p = 0.06). Eighty patients (more ...)
Asbestos body burden predicts survival in MPM, Cox’s proportional hazards model.