Letter: Craniotomy and Survival for Primary Central Nervous System Lymphoma

To the Editor:

We applaud Rae et al¹ for a recent publication of a retrospective study focusing on primary central nervous system lymphoma (PCNSL). In the study, the authors compared patients with PCNSL who received biopsy to those who received craniotomy using the National Cancer Database (NCDB).¹ However, NCDB does not contain data on cause-specific survival, and consequently, the study was limited in that aspect. Therefore, it is uncertain to what extent is PCNSL relevant to the death observed, and if PCNSL contributes to mortality differently in patients who received biopsy versus those who received craniotomy.

We identified 9250 patients with PCNSL diagnosed from 2004 to 2014 from the NCDB who received biopsy (n = 5775) or craniotomy (n = 3475), based on the exact inclusion criteria as presented in the study by Rae et al.¹ We analyzed the survival of all PCNSL patients, as well as subgroups of patients stratified by treatment, relative to that of the age- and gender-matched US general population, in order to compensate for the fact that information on cause-specific survival was unavailable. The strs command in STATA/SE 13 (Stata Corportaion, College Station, Texas) was used to analyze relative survival, a method described by P.W. Dickman et al. in the Stata Journal.² The age- and gender-matched portion of the US general population was obtained yearly from the US Census Bureau (www.census.gov). The mortality data of the same subgroups of the population was extracted from the Centers for Disease Control and Prevention (www.cdc.gov). The 5-yr relative survival compared to the expected survival of an age- and gender-matched US population was 33.5% (95% confidence interval [CI] 32.2%-34.7%; Figure 1A), suggesting that PCNSL is a significant component of mortality.

FIGURE 1.: Survival relative to age- and gender-matched US general population with 95% confidence interval for A, the entire cohort and B patients who received biopsy alone or craniotomy.

We also performed analyses on the overall and relative survival in subgroups of patients receiving either biopsy or craniotomy. Similar to the study by Rae et al,¹ the median overall survival (OS) was 10.8 mo (95% CI 9.8-11.8) for patients who received biopsy, and 19.8 mo (95% CI 17.4-22.3) for patients who received craniotomy, and there is a significant difference in OS between patients who received biopsy and those who received craniotomy (log-rank test, P < .0001). The 5-yr relative survival rate for patients who received biopsy was 31.0% (95% CI 29.5%-32.5%), and for patients who received craniotomy was 37.6% (95% CI 35.5%-39.5%; Figure 1B).

In conclusion, PCNSL contributed significantly to mortality in affected patients who received biopsy or craniotomy, as indicated by the relative survival analysis. We believe that our analysis accounted for the deficient of cause-specific survival data and compensated for a significant limitation of the Rae et al¹ study.

Disclosure

The authors have no personal, financial, or institutional interest in any of the drugs, materials, or devices described in this article.