New vblog post [1] below.
(Dr. Myers seems unusually animated. Perhaps in a rush to go off somewhere for July 4th?)
I have never used aspirin for PCa, & I would never use low-dose aspirin on a daily basis, so I might be thought to be biased against aspirin. But there is a case to be made for aspirin in PCa. (Although there is a better alternative IMO,)
The connection has to do with abnormal coagulation in cancer cases & the relationship between clotting and metastasis.
Two things happen as a clot is formed: (1) aggregation of platelets to form a plug & (2) accretion of fibrin to build the clot. Aspirin inhibits the aggregation of platelets. & this happens at low doses (no advantage in higher doses.) Thus, in my view, studies that find better PCa survival in chronic low-dose aspirin users, have a certain degree of plausibility. Just as studies that associate warfarin with benefit do.
Dr. Myers says that PCa-aspirin studies are so mixed that perhaps some men benefit & some do not. If aspirin is beneficial because it reduces clot-related metastases, it would benefit the entire population of cases.
Myers points to a TMPRSS2:ERG fusion study [2], where aspirin use seems to have reduced the percentage of fusion-positive cases. OK, that is a bonus, but it certainly does not explain why the PCa-aspirin studies are mixed. The benefit should show up in each study, assuming that fusion risk was similar in each population.
It so happens that a useful cancer-aspirin meta-analysis was published in April [3]:
"Aspirin in the Treatment of Cancer: Reductions in Metastatic Spread and in Mortality"
Here's what it says about PCa:
... input: "ten {observational studies} on prostate cancer mortality"
"Heterogeneity between nine studies of prostate cancer was significant, but ... the omission of one study led to acceptable homogeneity"
"Amongst ten studies of aspirin and prostate cancer [44–53] nine give a cause specific mortality of 0.94 ... with significant heterogeneity, Sensitivity analyses indicated that one study is responsible [44] and its omission led to an HR of 0.89 ..."
i.e. an 11% reduction in mortality.
"An effect of aspirin on metastatic spread is clearly an evidence of treatment and the data in Table 4, although sparse, are therefore of considerable importance. Two studies of breast cancer [14,46], two of prostate [23,38] and one of both cancers together with colon [4], give evidence of a reduction in spread by aspirin."
"Data in three reports of prostate cancer suggest that the effect of aspirin may be greater in advanced disease. ..."
"Several authors state that an effect of aspirin because apparent only after 3–5 years of therapy. Goh et al [26] state that they found evidence of benefit only after 5 years, Stock et al [53] who reported no benefit to prostate cancer overall (HR 1.03 ...) states that after five years of aspirin taking there was benefit (HR 0.54 ...) and an effect of aspirin taking in the study of lung cancer [55] became significant only after three years (HR = 0.84 ...)."
That last paragraph is probably discouraging to those with significant mets, but, just as in studies that show an advantage in eliminating the primary tumor even after metastasis has occurred, there might be some benefit in reducing further mets.
In the study cited by Dr. Myers:
"T2E {TMPRSS2:ERG} fusion was present in 171 (49%) cases, with younger cases more likely to be fusion positive ... Current aspirin use was associated with a 37% risk reduction of T2E-positive tumors"
This U.S.-German study did not address survival. Dr. Myers has made an uncharacteristic leap, I feel, but it is an interesting study. Just why aspirin would make a difference isn't explored in the Abstract. The reference to inflammation seems spurious, considering that no other NSAID had a similar effect.
Myers has never used aspirin in his practice & has witnessed a certain amount of morbidity in patients who are users. Perhaps he would now consider it in fusion-positive cases?
-Patrick
Snuffy Myers on Metformin 
Cohort study of aspirin use among African Americans
Weekly aspirin cuts cancer risks
Possible Aspirin Help in Reducing Cancer Mortality
