Toon Van Gorp, MD, PhD, University Hospital Leuven, Belgium, discusses the final analysis of the phase 3 MIRASOL trial, evaluating mirvetuximab soravtansine compared with investigator’s choice of chemotherapy among patients with folate receptor alpha (FRα)-positive, platinum-resistant ovarian cancer. The primary analysis from MIRASOL reported that mirvetuximab demonstrated a significant improvement of investigator-assessed progression-free survival (PFS), investigator-assessed objective response rate (ORR), and overall survival (OS).

Dr Van Gorp concluded, “When we look at the efficacy, the fact that this benefit in overall survival, progression-free survival, objective response rates, duration of response, is all maintained with a very long follow-up, means that [mirvetuximab soravtansine] is really the best treatment to give for these patients in the platinum-resistant setting.”

These results were first presented at the 2025 Society of Gynecologic Oncology (SGO) Annual Meeting on Women’s Cancer in Seattle, Washington.

Transcript:

Hello. Hi, I'm Toon Van Gorp. I'm a gynecological oncologist from Leuven in Belgium. I'm also the current chair of the BGOG, which is the Belgian oncology group. And I'm here to discuss with you the final overall survival results of the MIRASOL study, which was a phase 3 study investigating mirvetuximab soravtansine versus investigator’s choice chemotherapy in folate receptor alpha-positive, high-grade serous platinum-resistant ovarian cancer.

The primary results of this study were already presented at ASCO 2023 by my colleague Dr Kathleen Moore [University of Oklahoma Health Sciences Center], who was actually also the global co-lead of this study. And back then we had a positive result for overall survival, progression-free survival, and also the objective response rate. What I am going to explain today is that we now have the final analysis of the MIRASOL study. The primary analysis was done after a follow-up time of 13.1 months. And the final analysis is now at after 30.5 months, which is actually one of the longest follow-up times that we have ever seen in any of the global studies in platinum-resistant ovarian cancer.

First of all, I want to recap a little bit the design of the study. It was a global, open-label, phase 3 study, and patients were randomized 1-to-1 between mirvetuximab or investigator's choice chemotherapy. And patients were allowed when they had a positive folate receptor alpha test, which is in about 35% of patients, and also 1 to 3 prior lines were allowed. The primary end point is progression-free survival as assessed by the investigator and the key secondary end points were overall survival and also objective response rates.

When we look at the results of the final analysis, we see that there is still a benefit for mirvetuximab over investigator’s choice chemotherapy with a hazard ratio of 0.68. This means that there is a 32% reduction for the risk of death when we use mirvetuximab. And when you look at the curves, you see that the curves split quite early on, and they stay separated along the whole evolution of the curve. This means that we don't have banana curves, the survival doesn't come back together again, so this is a very prolonged overall survival benefit. The median overall survival for mirvetuximab soravtansine was 16.9 months, and for investigator’s choice chemotherapy is 13.3 months — a clear benefit for mirvetuximab.

The next thing that we looked at was progression-free survival, and there again we had a benefit with a hazard ratio of about 0.63, a risk reduction of 37% for progression or death. Again, this benefit was maintained. And also when we looked at the other end points like objective response rate, duration of response, and also PFS-2, we still see that mirvetuximab keeps on having the biggest benefit, patients that receive mirvetuximab soravtansine have the biggest benefit when they are treated with mirvetuximab soravtansine. And to give you one example, PFS-2, for example. For PFS-2, we look at the benefit after progression on mirvetuximab, after the first progression, and there we also see a hazard ratio of 0.59.

Of course, besides efficacy, we also have to look at safety because after the first analysis, we want to know is there any additional risks when patients continue for a very long time with mirvetuximab. And what we saw right there was that again, mirvetuximab had less grade 3 or higher treatment-emergent adverse events, also less serious adverse events, and also less adverse events leading to discontinuation of the drug, which is important. Almost double the number of patients that received chemotherapy. When we look at the number of patients that had to stop, the number of patients that needed to stop due to the treatment was twice as high when they received chemotherapy.

Of course, there are treatment-related adverse events, and if I want to go over them a little bit, we see that there is less hematological adverse events or less hematological adverse events when we give mirvetuximab. We do see some neuropathy, but it's less severe compared to paclitaxel, and it's mainly grade 1 and 2. We don't hardly see any alopecia; that's really important for our patients. And we do see gastrointestinal adverse events, like nausea and diarrhea, and they are a little bit the same as with chemotherapy. Of course, the last one is the ocular toxicity. This is something which is very typical for mirvetuximab, and this is more prominent when we use mirvetuximab, we know this. It's mainly grade 1 and 2. We have a mitigation strategy to counter this, and of course, whenever it's necessary, you can do those adaptations.

In conclusion, first of all, mirvetuximab soravtansine is one of the first treatments that was a novel treatment that was able to do better than chemotherapy over the last decades. This is the first thing. And the second thing is that when we look at the efficacy, the fact that this benefit in overall survival, progression-free survival, objective response rates, duration of response, is all maintained with a very long follow-up, means that this is really the best treatment to give for these patients in the platinum-resistant setting. And moreover, it's also a safe treatment. When we look at the safety data, there are less serious adverse events, grade 3 or higher adverse events. This means that this is, again, an additional argument to use mirvetuximab for the patients that have folate receptor alpha-high, platinum-resistant ovarian cancer. And I think with all this information, this makes this the standard of care for these patients. Thank you.

Source:

Van Gorp T, Angelergues A, Konecny G, et al. Final overall survival analysis among patients with folate receptor alpha-positive, platinum-resistant ovarian cancer treated with mirvetuximab soravtansine versus investigator’s choice chemotherapy in phase II MIRASOL (GOG-3045/ENGOT-ov55) study. Presented at the 2025 SGO Annual Meeting on Women’s Cancer. March 14-17, 2025; Seattle, WA. Abstract 939696.