Retroperitoneal sarcomas: the benefits of radiotherapy

Sarcomas are a rare form of cancer, with around 5,000 cases occurring every year in France. Retroperitoneal sarcomas are a sub-type of this form of cancer, and present even fewer cases: around 500 per year. These figures are low when compared to the 50,000 annual breast or prostate cancer cases, and for patients, this is a serious issue: it means very few forms of treatment have been approved.

Retroperitoneal sarcomas occur in the abdomen, on or within various organs such as the kidneys, colon, or some muscles. They form significant masses, as they become symptomatic at a very late stage. Until now, standard treatment for these types of cancer took the form of surgery on the original tumor.

The average size of these tumors upon diagnosis is around 25cm, and it isn’t rare to operate on abdominal sarcomas ranging from 30 to 40cm

explains Sylvie Bonvalot, an Institut Curie surgeon who specializes in these forms of cancer. The challenge lies in removing the tumor in a single piece, as well as the healthy tissue surrounding it to ensure no cancerous cells remain in the area. But despite surgeons’ expertise and the precautions they take, even in highly specialized centers, the local recurrence rate for this type of cancer remains around 30% in the five years following surgery. And some cancers reoccur even later.

Last year at ASCO, we used a national study to demonstrate that early surgical treatment in an expert center specializing in sarcomas improved general survival rates

highlights Sylvie Bonvalot.

Along with her European and American colleagues, the surgeon is attempting to improve the effectiveness of treatments. But conducting clinical trials on such rare forms of cancer is particularly complex, as researchers need to recruit a sufficient number of patients who meet all the right criteria, and who agree to take part in the trial, in order to extract pertinent findings. The result is that it took five years, from 2012 to 2017, to bring together 266 patients with an initial retroperitoneal sarcoma in this first international randomized trial for this type of cancer, thanks to cooperation from around thirty centers in Europe, the United States and Canada, and with the support of the EORTC, the European Organisation for Resarch and Treatment of Cancer. Half of the patients received the standard treatment (surgery alone), while the other half underwent neoadjuvant (pre-operative) radiotherapy before surgery, in the hope of weakening the cancer cells as far as possible before removing their tumors. Two years on, the time came to assess the results. Sylvie Bonvalot, who coordinated the entire trial, is presenting her findings at the ASCO Annual Meeting’s sarcoma presentation session.

For the time being, this combination of radiotherapy and surgery did not provide any significant advantage for patients as a whole, all retroperitoneal sarcomas combined. However, patients with liposarcomas (sarcomas occurring in fat cells) saw their local recurrence rates halve. We currently have an average follow-up of 43 months, and we know that recurrence tends to occur late with this illness. By continuing to monitor any potential recurrences over the next few years, we may be in a better position to assess the results of radiotherapy across all patients who took part in the study. In the meantime, these findings are a good starting point for helping clinicians decide which of their patients may benefit from pre-operative radiotherapy

says Dr. Bonvalot