Genetic and metabolic predictors of chemosensitivity in oligodendroglial neoplasms

Dynamic susceptibility contrast and diffusion MR imaging identify oligodendroglioma as defined by the 2016 WHO classification for brain tumors: histogram analysis approach

PURPOSE

According to the revised World Health Organization (WHO) Classification of Tumors of the Central Nervous System (CNS) of 2016, oligodendrogliomas are now defined primarily by a specific molecular signature (presence of IDH mutation and 1p19q codeletion). The purpose of our study was to assess the value of dynamic susceptibility contrast MR imaging (DSC-MRI) and diffusion-weighted imaging (DWI) to characterize oligodendrogliomas and to distinguish them from astrocytomas.

METHODS

Seventy-one adult patients with untreated WHO grade II and grade III diffuse infiltrating gliomas and known 1p/19q codeletion status were retrospectively identified and analyzed using relative cerebral blood volume (rCBV) and apparent diffusion coefficient (ADC) maps based on whole-tumor volume histograms. The Mann-Whitney U test and logistic regression were used to assess the ability of rCBV and ADC to differentiate between oligodendrogliomas and astrocytomas both independently, but also related to the WHO grade. Prediction performance was evaluated in leave-one-out cross-validation (LOOCV).

RESULTS

Oligodendrogliomas showed significantly higher microvascularity (higher rCBV_Mean ≥ 0.80, p = 0.013) and higher vascular heterogeneity (lower rCBV_Peak ≤ 0.044, p = 0.015) than astrocytomas. Diffuse gliomas with higher cellular density (lower ADC_Mean ≤ 1094 × 10^-6 mm²/s, p = 0.009) were more likely to be oligodendrogliomas than astrocytomas. Histogram analysis of rCBV and ADC was able to differentiate between diffuse astrocytomas (WHO grade II) and anaplastic astrocytomas (WHO grade III).

CONCLUSION

Histogram-derived rCBV and ADC parameter may be used as biomarkers for identification of oligodendrogliomas and may help characterize diffuse gliomas based upon their genetic characteristics.

Relative survival of patients with supratentorial low-grade gliomas

We sought to assess the population-based estimates of age-standardized survival among patients with low-grade gliomas (LGG) and to determine the impact of age and time on relative survival (RS). Data from the Surveillance, Epidemiology, and End Results (SEER) program of NCI from 1973 through 2006 were analyzed to assess survival among 5037 patients. Relationships were modeled using Dickman's piecewise constant hazards RS model. The 3- and 10-year age-standardized RS were 67% and 37%, respectively. When analyzed by age group, the 10-year overall survival (OS) and RS for children (age, <16 years), young adults (age, 16-39 years), adults (age, 40-64 years), and older patients (age, ≥65 years) were 86% and 86%, 61% and 62%, 40% and 43%, and 10% and 14%, respectively. The observed difference between OS and RS was larger among older patients (4%) and smallest among children (<1%). Older patients were 30.5 times (excess hazard ratio [eHR]; 95% confidence interval [CI], 20.3-50.0) as likely as young adults to die during the first year and 18.2 times as likely to die during the second year. Adults were 5.3 (eHR; 95% CI, 3.5-8.1) times as likely to die during their first year as young adults. In the remaining years, the observed survival differences were substantially decreased, and the presence of an age-by-follow-up interaction was observed. Survival among older patients with LGG was substantially different from the one computed for young adults and children. Despite the hazards across age groups not being proportional, RS does not provide additional information, compared with OS, in patients with LGG.

Cellularity and apparent diffusion coefficient in oligodendroglial tumours characterized by genotype

PURPOSE

Apparent diffusion coefficient (ADC) describes water diffusion within tissues. Previous studies report a negative linear correlation between minimum ADC and tumour cellularity in different types of gliomas, but there are no studies in oligodendroglial tumours. This study evaluated the relationship between ADC and tumour cellularity in oligodendroglial tumours characterized by genotype.

METHODS

ADC was assessed in 17 patients with known 1p/19q status: 3 grade II oligodendrogliomas (OII), 9 grade II oligoastrocytomas (OAII), 5 grade III oligoastrocytomas (OAIII). Regions of interest were placed on ADC maps around tumour margins to generate mean tumour ADC, and over minimum and maximum tumour ADC. Histopathology assessment of tumour cellularity determined minimum, maximum and mean cell density in serial stereotactic biopsies.

RESULTS

1p/19q loss was present in 2/3 OII, 5/9 OAII, 2/5 OAIII. Grade III tumours had higher maximum cell density than grade II tumours (17.2 vs. 10.57%: Mann Whitney U; P = 0.20). Oligoastrocytoma were more likely to have a lower minimum cell density than oligodendrogliomas (Mann Whitney U; P = 0.032). There was no relationship between cell density and genotype. There was no linear correlation between mean ADC and mean cell density (Spearman's rho; r = 0.486: P = 0.438), minimum ADC and maximum cell density (Spearman's rho; r = 0.158: P = 0.660), and maximum ADC and minimum cell density (Spearman's rho; r = 0.039: P = 0.985).

CONCLUSIONS

In oligodendroglial tumours there is no relationship between quantitative assessment of cellularity and ADC. This may reflect differences in oligodendroglial tumour biology compared to other gliomas, although the composition of the extracellular matrix may influence ADC more than cellularity.