The effects of tumor size and postoperative radiotherapy for patients with adult low-grade (WHO grade II) infiltrative supratentorial astrocytoma/oligodendroglioma: A population-based and propensity score matched study

Abstract

Background: The update of 2018 NCCN guidelines (central nervous system cancers) recommended the risk classification of postoperative patients diagnosed as adult low-grade (WHO grade II) infiltrative supratentorial astrocytoma/oligodendroglioma (ALISA/O) should take tumor size into consideration. Moreover, the guidelines removed postoperative radiotherapy (PORT) for low risk patients. Our study aimed to explore the specific tumor size to divide postoperative patients into relatively low- or high risk subgroups and the effect of PORT for ALISA/O patients.

Methods: We conducted a retrospective study choosing 1277 postoperative ALISA/O patients from the Surveillance, Epidemiology, and End Results database. The X-tile analysis provided the optimal cutoff point based on tumor size. The differences between surgery alone and surgery +RT groups were balanced by propensity score-matched analysis. The multivariable analysis and the nomogram evaluated multiple prognostic factors based on cancer-specific survival (CSS) and overall survival (OS).

Results: X-tile plots defined 59 mm (P < 0.001) as the optimal cutoff tumor size value in terms of CSS, which was verified in multivariate analysis (P < 0.001). The Kaplan-Meier analysis showed that the surgery alone had higher CSS and OS than surgery +RT, while the low risk group had no statistical significance after propensity score match. Multivariable analysis showed that surgery +RT was independently associated with diminished OS and CSS for high risk group, which had no statistical significance for low-risk group.

Conclusions: Our study suggested that tumor size of 59 mm was an optimal cutoff point to divide postoperative patients into relatively low- or high risk subgroups. PORT may not benefit patients, while the effects of PORT for low risk patients need further research.

Keywords: Epidemiology; Surveillance; and End Results; astrocytoma/Oligodendroglioma; low-grade (WHO grade II); postoperative radiotherapy; propensity score match; tumor size.

Figure 1

Overall (A) and cancer–specific (B) survivals in all patients with adult low‐grade (WHO grade II) infiltrative supratentorial astrocytoma/oligodendroglioma (ALISA/O) undergoing surgery alone or surgery +RT. CSS, cancer‐specific survival; HR, hazard ratio; OS, overall survival; RT, radiotherapy

Figure 2

X‐tile analysis of survival data from the SEER registry reveals a continuous distribution based on tumor size, equally divided into training and validation sets. A shows tumor size divided at the optimal cut‐point, as defined by the most significant (brightest pixel) on the plot (59 mm, P < 0.0001). Diffuse red indicates a continuous indirect association between increasing tumor size and good prognosis. B shows the cut‐point on a histogram of the entire cohort. Kaplan‐Meier analysis is provided to analyze overall (C) and cancer–specific (D) survivals based on optimal tumor size cutoff point in the whole cohort. P values were determined using the cutoff point defined in the training set and applying it to the validation set. (The optimal cutoff value for tumor size is 59 mm, χ2 = 50.107, P < 0.001). CSS, cancer‐specific survival; HR, hazard ratio; OS, overall survival.

Figure 3

Kaplan‐Meier survival curves illustrating ALISA/O overall and cancer‐specific survival between the surgery alone and surgery +RT groups for low‐ (A and B) and high‐risk (C and D) patients before propensity score matching. CSS, cancer‐specific survival; HR, hazard ratio; OS, overall survival; PSM, propensity score matched; RT, radiotherapy.

Figure 4

Kaplan‐Meier survival curves illustrating ALISA/O overall and cancer‐specific survival between the surgery alone and surgery +RT groups for low‐ (A and B) and high‐risk (C and D) patients after propensity score matching. CSS, cancer‐specific survival; HR, hazard ratio; OS, overall survival; PSM, propensity score matched; RT, radiotherapy

Figure 5

A cancer‐specific survival nomogram for high risk patients with ALISA/O. To use the nomogram, an individual patient's value is located on each variable axis, and a line is drawn upward to determine the number of points received for each variable value. The sum of these numbers is located on the Total Points axis, and a line is drawn downward to the survival axes to determine the likelihood of 1‐, 3‐, or 5‐year survival

Figure 6

The calibration curve for predicting patient survival at (A) one year, (B) three year, and (C) five year in the primary cohort. Nomogram‐predicted probability of cancer‐specific survival is plotted on the x‐axis; actual cancer‐specific survival is plotted on the y‐axis