Published in Oncology News · March 20, 2020 HOPA 2020: Metformin Shows Signs of Benefit in Metastatic Prostate Cancer

[Balsam01]

March 13, 2020—Tampa, Florida—Though no significant differences were found in 6-month PSA response or progression-free survival, a significant difference in overall survival was observed among patients who took metformin for metastatic prostate cancer.

This outcome of a single-center, retrospective review was reported at the Hematology/Oncology Pharmacy Association’s 16th Annual Conference (HOPA), from March 11–14.

So Yi Lam, BS, of St. John's University, Queens, New York, and colleagues set out to investigate the significance of adding metformin to treatment for prostate cancer.

Patients with metastatic prostate cancer patients between 2014 and 2017 at Ms. Lam’s center were categorized as suffering from metastatic castration-resistant or metastatic hormone-sensitive prostate cancer.

Within these groups, they were stratified further according to whether they received or did not receive metformin.

Radiological progression-free survival was evaluated based on criteria of the Prostate Cancer Working Group 3 and Response Evaluation Criteria in Solid Tumors. The 6-month PSA response and overall survival were also evaluated.

A total of 281 subjects with a minimum of 3 months' follow-up were included for analysis (mean age, 70 ±10 years).

Patients were known to suffer from either metastatic hormone-sensitive (n = 205; 73.2%) or metastatic castration-resistant (n = 75; 26.8%) prostate cancer.

Overall, 66 patients took metformin (23.5%); 215 did not (76.5%). No significant difference was observed between metformin groups with respect to PSA response at 6 months.

Among those with a recorded 6-month PSA response, 70.4% (38 of 54) responded in the metformin group; 72.9% (140 of 192) in the non-metformin group.

Overall median progression-free survival was estimated to be 17 months.

No significant difference in progression-free survival was observed between metformin groups (16.6 vs 17.3 months).

Within the group with metastatic hormone-sensitive prostate cancer, metformin users were at lower risk of progression (11% risk reduction; not statistically significant) relative to nonusers (hazard ratio, 0.89; 95% confidence interval, 0.62-1.29).

Within the group with metastatic castration-resistant prostate cancer, metformin users were at significantly higher risk of progression vs nonusers (hazard ratio, 2.65; 95% confidence interval, 1.4-5.0).

Median overall survival was estimated to be 81.5 months. Overall survival differed significantly between metformin groups (148.5 vs 69.4 months, respectively; P = .02).

Ms. Lam explained that prostate cancer is the third most common cancer, with 31,620 estimated deaths and 174,650 estimated new cases in the US in 2019.

Treatments for metastatic prostate cancer are mainly hormone therapy and chemotherapy. Metformin, a biguanide, is the most widely prescribed antidiabetic drug worldwide due to its clinical effectiveness and tolerability. Metformin was suggested to possibly reduce insulin-stimulated cancer growth in 2008.

Large observational studies on commonly diagnosed cancers found inverse associations between metformin use and colon cancer, liver cancer, and lung cancer.

Findings of epidemiologic studies on the association of metformin use with prostate cancer risk have been inconsistent, however. Although significant inverse relationships between metformin therapy and the risk of prostate cancer have been reported, numerous other epidemiological studies failed to demonstrate this association.

Meta-analyses have been performed on this topic, indicating a protective effect of metformin use on the risk of prostate cancer. Cohort studies yielded inconsistent results.

Ms. Lam concluded that no significant differences were found in 6-month PSA response or progression-free survival between patients with metastatic prostate cancer who took vs did not take metformin.

A significant difference in overall survival, however, was observed between patients who did vs did not take metformin.

[Schwah]

I’m confused. You say “metformin users were at significantly higher risk of progression vs nonusers (hazard ratio, 2.65; 95% confidence interval, 1.4-5.0).” So that’s bad for metformin use, right ?

But then you say:

“Overall survival differed significantly between metformin groups (148.5 vs 69.4 months, respectively; P = .02”

so that’s good for metformin use, right ?

How could metformin users be both at a “higher risk of progression” and also survive “148.5 months vs 69.4 months” for non users. Am I reading this wrong ?

Schwah

[Don_1213 in reply to Schwah]

I don't know who "you" is that you're addressing... but to me this brings the thought that the metformin group was a higher-risk group than the non-metformin group. This is BEFORE the study started with people taking metformin.

The second statement said the higher-risk-of-progression metformin users lived longer, Entirely possible if metformin is doing any good.

The entire summary(?) is a very poorly written article. It appears besides meformin users, there are sub-categories of metformin users, at least that's what the text implies.

Hopefully if one was to see the actual study this article is based on it might become clearer. As the article is written - I think it's a waste of time trying to figure out what it's saying since it appears the author is confused with what they are trying to say.

[GeorgesCalvez]

My blood sugar was around 1,35 g/L before I started Firmagon, it rose to 1,70 g/L while I was on Firmagon and gradually declined after I started a regime of Irbesartan and 2 times 500mg of metformin a day, six months off Firmagon and it is down to around 1,15 - 1,20g/L in the mornings and my PSA remains undetectable.