Two new blockbuster studies on treating cervical cancer serve as a warning—when it comes to medicine, newer is not always better.

Background: Radical hysterectomy—the complete removal of the uterus and cervix as well as some surrounding tissue—is the gold standard for treating early stage cervical cancer, with an expected cure rate well over 80%. Before 2006, most radical hysterectomies were done through a large, open incision. But since then, many surgeons have moved to minimally invasive laparoscopic surgery with its small keyhole incision, sometimes using robotic arms to control the laparoscopic tools.

Minimally invasive techniques for many types of surgery have become popular because they offer shorter recovery and a slightly reduced risk for complications such as bleeding, swelling in the legs and sexual or bladder dysfunction. The benefits for cervical cancer in particular led the National Comprehensive Cancer Network, an alliance of 27 outstanding US cancer centers, to change its guidelines to state that both minimally invasive laparoscopic surgery and open surgery were appropriate. And in short order, laparoscopic became the dominant choice. However, there were few large or long-term studies at the time to support this preference.

Both of the new studies set out to compare results of the old and new surgeries. One, led by researchers at MD Anderson Cancer Center in Houston, looked at disease-free survival (meaning no signs or symptoms of the cancer) and overall survival. Participants included 600 women with early stage cervical cancer. Half had minimally invasive surgery, the other half had open surgery. After 4.5 years, the open group had a 96.5% disease-free rate compared with 86% for the minimally invasive group. They also had a higher overall survival rate—99% compared to 93.8% after three years.

The second study analyzed the mortality rates of women undergoing cervical cancer surgery at leading cancer centers and university hospitals using two timeframes. First, they used a large cancer registry to track women for four years. They looked at about 2,500 women with early cervical cancer evenly divided between open and minimally invasive surgery during 2010 and 2013. Once again, open surgery was better for survival—the four-year mortality rate was 5.3% among open surgery patients, but 9.1% among the minimally invasive group.

These researchers also took a longer view, going back to mortality rates between 2000 and 2010. They found that before 2006, when open surgery dominated, survival rates remained stable. But after 2006, when minimally invasive surgery became dominant, they saw a gradual drop in the survival rate of close to one percentage point.

Why exactly minimally invasive surgery reduces survival isn’t clear. It could be because it’s harder to move the uterus into position for removal. This may result in smaller tumor-free margins—the amount of tissue beyond the cancer target that is removed to increase the chance of removing all cancer cells. The instrument used to move the uterus might increase the amount of tumor cells that “spill” or escape into the body during surgery. Some studies suggest that CO2 gas used to inflate the abdomen before laparoscopic surgery may stimulate tumor cells.

While these studies may not result in the end of minimally invasive surgery for cervical cancer, it’s important to be aware of their significant findings when considering surgery choices and to discuss them in depth with your oncologist.