Metformin in lieu of ADT in SRT - Low/Intermediate Risk

The two existing phase III trials show a benefit for combining SRT with ADT for high risk patients only. With a Gleason 6 your are definitely not high risk.

I would not start with SRT before the PSA value gets above 0.1 ng/ml. In your case it will probably take a year and a half to reach that value. It may even stabilize below that.

George

There has been a randomized clinical trial that proved that 6 mos. of adjuvant ADT with SRT is better than none. An earlier clinical trial (RTOG 9601) showed a benefit to years of bicalutamide vs none. These, and other retrospective studies are discussed here:

/pcnrv.blogspot.com/2016/08/combining-androgen-deprivation-therapy.html

However, in a retrospective study, researchers identified a group of patients in whom adjuvant ADT could safely be avoided. They found that it could be avoided in men with the following characteristics:

• Only those with a 10-year probability of distant metastases (based on PSA at the time of SRT) greater than 1 in 3 benefited from the addition of ADT
• The benefit grew exponentially with increasing risk
• Adjuvant ADT only benefited those with higher PSA (≥0.4 ng/ml), Gleason score 8-10, stage T3b/4.
• Higher SRT dose and whole pelvic SRT improved outcomes independently of whether adjuvant ADT was used.

/pcnrv.blogspot.com/2018/01/when-can-adt-be-safely-avoided-with.html

This begs the question of whether you need SRT at all. Based on your Decipher score, favorable disease characteristics, and very slow increase in PSA, I think you should hold off until you have a consistent pattern of increasing PSA. It is likely that some small amount of Gleason 6 was left behind, and most Gleason 6 never needs treatment:

/pcnrv.blogspot.com/2017/11/myth-gleason-6-never-progresses.html

Metformin has few side effects and is one of the oldest drugs around, so unless you are one of the few allergic to it, the cost/benefit is definitely favorable. ADT with SRT is at the point where clinical trials show it's generally helpful, but with G6 they are not that sure. So it depends on your tolerance for temporary side effects. For me, a G7 with no adverse pathology, I would definitely do it because i'd rather be safe than sorry and am willing to tolerate some temporary discomfort.