Post-operative radiotherapy speeds recovery with MG due to thymoma

Radiation's use seen to ease MG symptoms in significantly shorter time

Patricia Valerio, PhD avatar

by Patricia Valerio, PhD |

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Radiotherapy given after surgery to remove the thymus, called a thymectomy, eases symptoms of myasthenia gravis (MG) associated with a thymus tumor, and it can cut in half the time to a considerable recovery, a study from China found.

Such recovery, known as minimal manifestation status, was defined as no MG-associated symptoms or functional limitations, but with some weakness in specific muscles upon examination.

The use of post-operative radiotherapy, or PORT, also was associated with better survival, including in patients classified as high-risk according to their thymoma, or thymus tumor, type.

Study findings “demonstrate that PORT can improve the symptoms and prognosis of [patients with] thymoma and MG,” the researchers wrote.

The study, “The value of post-operative radiotherapy in thymoma patients with myasthenia gravis,” was published in Radiotherapy and Oncology.

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An autoimmune disease, MG is caused by self-reactive antibodies that target and attack proteins of neuromuscular junctions, the sites of communication between nerve and muscle cells. Muscle weakness and fatigue are common disease symptoms.

Abnormalities in the thymus — a gland that is part of the immune system — are commonly seen in MG patients, with thymoma present in up to 20% of all cases.

A thymectomy is often a treatment of choice to manage MG, helping to reduce a reliance on disease-related medications and/or achieve stable remission. In combination with a thymectomy or after one, patients also may receive chemotherapy and/or radiation therapy (radiotherapy).

However, “few studies have explored the impact of radiotherapy on MG-related symptoms” and PORT’s use “remains controversial,” the scientists wrote.

Researchers in Hunan examined the potential value of PORT, in terms of symptoms and outcomes, among 126 patients with thymoma-associated MG who where followed for up to 12 years at their hospital.

All the patients, mostly (56.3%) women, had undergone a thymectomy. A majority, 72 people or 57.1%, also received post-operative radiotherapy (PORT group), while 54 did not (nonPORT group). Nine patients (7.3%) also were given chemotherapy.

Patients’ thymomas were divided into low-risk (A, AB, and B1) and high-risk (types B2 and B3) groups, according to World Health Organization criteria, and into different stages of tumor invasion (I to V; with I signifying a local cancer and V meaning metastases), according to the Masaoka-Koga Staging System.

PORT’s short-term efficacy, defined as within three months of surgery, was assessed through changes in quantitative MG (QMG) scores, which range from zero to 39, with higher scores indicating greater muscle weakness. A drop of three or more points can be considered clinically significant.

A total of 70 patients with available QMG scores, including 30 who received PORT, were included in this analysis.

QMG scores at three months after a thymectomy fell significantly among patients given PORT relative to their pre-surgery scores, from 10.2 to 6.2. No significant score changes were observed among patients not given PORT, moving from 9.2 to 8.3.

“Post-treatment QMG scores were lower in the PORT group than that in the non-PORT group,” the team wrote, adding that a significantly greater proportion of patients given PORT showed clinically significant score reductions (60% vs. 30%).

Minimal disease more likely, and more quickly, in patients given PORT

Minimal manifestation status was used to assess long-term changes in MG symptoms, with data available for all 126 patients.

Researchers found that a greater proportion of patients in the PORT group achieved this status than those not given PORT (63.9% vs. 40.7%) and in a significantly shorter time (two vs. 4.4 years). Receiving PORT was linked with a 97% increased chance of achieving the minimal manifestation status.

PORT also associated with significantly better disease-free survival — referring to time to tumor recurrence, metastasis, or death — with 95.8% of PORT-treated patients and 81.5% of those not given PORT remaining free of such events for more than five years after treatment.

A better 10-year overall survival rate also was seen among patients in the PORT group relative to the nonPORT group (94.4% vs. 85.1%), but this difference failed to reach statistical significance.

Significantly improved disease-free survival and overall survival also was evident among PORT patients with the high-risk B2 and B3 thymoma subtypes, and a significantly better disease-free survival for those with more advanced cancer (Masaoka-Koga stages II, III, and IV).

These findings “confirmed that PORT could improve both short- and long-term symptoms in these patients,” and that “PORT improved the survival among these patients,” the researchers wrote.

As such, “patients with thymoma and MG may benefit from PORT,” they added.

Results also suggest better outcomes for high-risk group patients with radiation therapy. The thymoma anatomy type “should be carefully considered in clinical management, including the design of adjunctive treatment trials and the determination of follow-up strategies,” the researchers wrote.

Further studies are needed to understand whether the easing in MG symptoms seen with PORT’s use associates with disease types, they added.