And in case it could not be possible to remove the entire tumour safely, patients survived significantly longer when surgery was followed by radiation therapy.
Gliomas are a type of brain tumor that form in the brain or spinal cord tissue and can spread within the nervous system. Low-grade gliomas are malignant and slow growing. Overall, patients' average survival is five to seven years after diagnosis, even with treatment.
"Mayo Clinic has a long history of expertise in treating patients with brain tumours. This makes our study unique in terms of the large volumes of patients seen here and the extensive length of follow-up," said Nadia Laack, M.D., a Mayo Clinic radiation oncologist and lead author of this study.
For the study, the researchers examined the records of 314 adult patients with low-grade gliomas who were diagnosed between 1960 and 1992 and had an average of 13 years of follow-up.
They found that almost half of the patients who underwent aggressive surgeries (gross total resection or radical subtotal resection) were free of tumour recurrence 15 years after diagnosis.
While performing aggressive surgery was not a safe option, postoperative radiation therapy nearly doubled average survival. The average survival time was three years in patients who did not receive radiation therapy, while those who had radiation therapy survived an average of six years.
"This study is exciting because it shows how well glioma patients can do after surgery. An average of 15 years tumor-free is better than any previously published results. It is also exciting to discover that patients can benefit from radiation therapy. It not only lengthens the time before the tumor comes back, it actually improves the length of time people live. This builds on previous Mayo Clinic data that suggested similar results from a small study published nearly 20 years ago," said Laack
Laack also said that the findings may be controversial due to common concerns about possible long-term side effects of radiation therapy.
She added that at Mayo Clinic, these potential side effects are minimized by tightly focusing radiation therapy on the tumour.
The study is available online as an advance publication in Neuro-Oncology.