Spontaneous Cancer Regression Extremely Rare

Megan Brooks

December 07, 2022

Spontaneous regression of solid tumors in the absence of anticancer treatment has been known to occur, but it is extremely rare, a new study confirms.

After pooling placebo response rates from 45 cancer drug trials in advanced solid tumors, researchers found a complete response of 0% and a partial response of 1%.

"Now we can answer our patients," tweeted lead investigator Bishal Gyawali, MD, PhD, of Queen's University, Kingston, Canada. Without treatment, "the chance of complete response is almost zero and should not be relied upon! It's next to a miracle.

"Hopefully, this data will convince our patients to not abandon cancer therapy," Gyawali added.

The study was published online late last month in eClinicalMedicine.

Bhavana Pothuri, MD, who was not involved in the research, was not surprised by the "very low rate" of partial and complete responses among patients who receive placebos.

This study provides "important information as we speak to patients" in trials and shows them the "substantial benefit" cancer treatments can provide, Pothuri, gynecologic oncologist at NYU Langone Perlmutter Cancer Center, New York City, told Medscape Medical News.

Fred R. Hirsch MD, PhD, agreed that the results were "interesting but not entirely surprising." The main message of this study "is cancer needs to be treated," said Hirsch, of the Tisch Cancer Institute at Mount Sinai, New York City, who was not involved in the study.

However, a recent national survey by the American Society of Clinical Oncology (ASCO) found that 40% of Americans believed their cancer could be completely cured with alternative treatments alone. This belief may be fueled by anecdotal reports shared among people with cancer, Gyawali noted in his tweet.

Concerned that such anecdotes might dissuade some patients from seeking treatment, Gyawali and colleagues sought to better understand the frequency with which advanced solid tumors undergo spontaneous regression.

The team analyzed placebo response rates in 45 randomized controlled trials in which cancer drugs were used to treat advanced solid tumors. The authors note that the "best estimate for the chances of spontaneous regression can be inferred through the placebo response rates in randomized trials since placebo, by definition, are inert substances that do not have any anti-tumor effects of their own."

The trials, published between 2015 and 2021, involved a total of 5684 patients. The authors clarified that placebo consisted of a monotherapy or best supportive care and was not used in combination therapy, such as chemotherapy or immunotherapy plus placebo.

Of the 4760 patients evaluable for an objective response rate in the placebo arm, 94 (1.97%) achieved an objective response. A pooled analysis revealed an objective response rate of 1%.

Of 3808 patients who could be evaluated for partial or complete responses, only four (0.1%) achieved a complete response. The pooled complete response rate was 0%. In addition, just over 2% of patients who received placebo (83 of 3808) achieved a partial response, with a pooled partial response rate of 1% across trials.

Gyawali and colleagues found it "reassuring" that their pooled placebo response rates were in line with those in two other studies, which showed an objective response rate of 2% with placebo or no active treatment among patients with advanced solid tumors.

"Thus, we can safely communicate with our patients that the chances of response without treatment is probably 1%, and not more than 2% even in the most optimistic scenario," the authors write.

The authors note, however, that subgroup analyses based on tumor types revealed slightly higher objective response rates in the placebo arm for prostate cancer (7%) and sarcoma (4%).

The higher objective response rate in prostate cancer might be explained by the therapeutic effect of prednisone or by the ongoing use of androgen blockade outside of the study.

"However, a 4% response rate in sarcoma patients is intriguing, and lacks clear explanation," the team writes.

Potential limitations of the study include possible publication bias and heterogeneity of studies evaluated.

Despite these limitations, Gyawali and colleagues conclude that patients "should not expect complete regression of cancers without treatment."

The study had no funding. Gyawali receives consulting fees from Vivio Health unrelated to this study. Hirsch and Pothuri have disclosed no relevant financial relationships.

eClinMed. Published online November 24, 2022. Full text

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