An oligodendroglioma is a brain tumor that arises from oligodendrocytes, cells that support and insulate nerve cells. These tumors are a subset of gliomas and often develop in the brain’s frontal or temporal lobes. In oncology, “recurrence” refers to the return of a tumor after initial treatment made it undetectable. Even after successful treatment, the cancer can reappear, a common characteristic of infiltrating gliomas like oligodendroglioma.
Defining Oligodendroglioma Recurrence Rates
Recurrence rates are statistical measures estimating the likelihood of a cancer returning after treatment, often calculated over 5 or 10 years. For oligodendrogliomas, these rates are influenced by the tumor’s grade, which reflects how quickly its cells grow. These statistics represent averages, and an individual’s outcome can differ based on many factors.
The rates differ significantly between low-grade and high-grade tumors, with nearly all oligodendrogliomas eventually returning over time. One study noted that 45% of patients with low-grade oligodendroglioma saw their tumor progress to a higher grade upon recurrence.
Key Factors Influencing Recurrence
Molecular Markers
Specific genetic signatures are significant predictors of oligodendroglioma behavior. The definitive molecular markers are a mutation in the IDH1 or IDH2 gene combined with a co-deletion of chromosome arms 1p and 19q. The presence of both the IDH mutation and the 1p/19q co-deletion defines an oligodendroglioma and is associated with a better prognosis.
These genetic markers indicate the tumor is less aggressive and more responsive to treatments like chemotherapy and radiation. This genetic information provides a more accurate prediction of tumor behavior than microscopic examination alone.
Extent of Surgical Resection
The goal of surgery for an oligodendroglioma is to remove as much of the tumor as safely as possible, as the amount removed is a strong predictor of time to recurrence. A gross total resection (GTR), where post-operative MRI scans show all visible tumor has been removed, is the objective. Achieving a GTR results in a significantly longer disease-free interval. A subtotal resection, where some tumor is left to avoid damaging healthy brain tissue, or a biopsy are associated with a shorter time to recurrence.
Tumor Grade
The grade of an oligodendroglioma is a primary factor in its likelihood of recurrence. These tumors are classified as Grade 2 (low-grade) or Grade 3 (anaplastic). Grade 2 oligodendrogliomas are composed of slow-growing cells, and while they tend to recur, the time to recurrence is often many years.
Grade 3 anaplastic oligodendrogliomas are more aggressive, with rapidly dividing cells, and they are considered malignant. This nature means they have a higher risk of returning, and the time to recurrence is shorter than for Grade 2 tumors. A Grade 2 tumor can also transform and recur as a higher-grade tumor.
Initial Adjuvant Treatment
Following surgery, adjuvant therapies are often used to manage remaining microscopic tumor cells and delay recurrence. The standard of care for many oligodendrogliomas, particularly Grade 3 and some Grade 2 tumors, involves combining radiation therapy and chemotherapy. Specific chemotherapy regimens, like procarbazine, lomustine, and vincristine (PCV) or temozolomide, have proven effective. These treatments target and destroy cancer cells that could not be removed surgically, extending the time before a potential recurrence.
Monitoring for Recurrence
After initial treatment, patients enter active surveillance to monitor for tumor recurrence. The primary tool for this is magnetic resonance imaging (MRI), which allows the medical team to spot new growth. The schedule for surveillance MRIs is more frequent in the first few years after treatment. A common protocol involves an MRI every 3 to 6 months for the first two to five years, after which the time between scans may be extended. This structured follow-up helps ensure that a returning tumor is detected as early as possible.
Patient-reported symptoms are also a component of monitoring, as neurological changes can be the first sign of a recurrence. Patients are encouraged to report any new or worsening symptoms to their healthcare team, such as:
- The return of seizures
- Persistent headaches
- New weakness or numbness
- Noticeable changes in cognitive function, like memory problems or personality shifts
Treatment and Prognosis After Recurrence
When an oligodendroglioma recurs, the new treatment plan depends on the patient’s health, the tumor’s location and size, and initial treatments. A second surgery to remove the recurrent tumor is often considered if it is safely accessible. If radiation was not used initially, it is a common option, while re-irradiation may be possible in certain circumstances. Second-line chemotherapy is also frequently used, which might involve a different drug or re-treating with the original agent if it was effective for a long period. Participation in clinical trials may also be an option.
The prognosis after a recurrence varies widely. Factors that influence the outlook include the time it took for the tumor to recur, as a longer interval is a more positive sign. The patient’s functional status and overall health at the time of recurrence are also important. The molecular characteristics of the recurrent tumor are also assessed, as favorable markers can indicate a better response to subsequent treatments.