What I’ve seen is that prostate cancer cells have higher levels of sarcosine - and this was researched as a potential test for prostate cancer.
The authors have not suggested that sarcosine causes prostate cancer but rather have demonstrated quite the opposite—that cancerous (or precancerous) prostate cells cause elevated levels of sarcosine. We would note in passing that the genetic inability to properly eliminate sarcosine (sarcosinemia) is biochemically recognized to occur in humans but is not associated with any recognizable phenotypic abnormality and is not known to be associated with malignancy of any type.
There is some suggestions that higher levels of sarcosine could be something that prostate cancer cells can feed off of, so if an older man has prostate cancer (only men have prostates, and cancer typically only happens in older men over the age of 65), he probably shouldn’t take sarcosine.
“Sarcosine levels seemed to control the invasiveness of the [prostate] cancer”