Welcome @bud3. You ask a good and commonly asked question among men who have had a prostectomy for prostate cancer. For this reason, I moved your post to this exising discussion:
- Post prostatectomy: What do rising PSA levels mean?: https://connect.mayoclinic.org/discussion/post-prostatectomy/

You will find many helpful responses from fellow members like @kujhawk1978 @web265 @spryguy @dandl48 @hoard @horace1818 @oumike @itterac and many more.

As to your question about level of concern, I would say you can have confidence in the fact that your doctor is being thorough. Are you able to put concern out of your mind until you have more information?

Well, the .3 meets the criteria for a BCR, a 2nd one in six weeks will confirm the BCR.

Attached is my clinical history. I remember well, the moment 15 months after a very "successful " surgery and pathology report (or so my urologist said, me, looking at the pathology report, GS 8, T2CNoMx, thinking the GS8 means I have a 30% probability my PCA returns and the Mx, meaning they don't know if it has spread already, in part because of micro-metastatic disease too small to be seen by any imaging, especially in 2015!).

I had my pity party, picked myself up off the floor and got to work learning all I could about BCR, standard of care and emerging clinical trials that might play a role in my treatment decision.

What I learned, the standard of care was SRT to the prostrate bed, 39 treatments, 70 or so Gya...emerging clinical trials indicated something different. Mayo was accumulating data showing when there was BCR and when SRT failed, it was because the PCa had already infiltrated to the PLNs. Their data indicated that often, the PLNS where the recurrence was were outside standard treatment fields for whole PLN radiation treatment. Data from clinical trails was showing that the addition of six months ADT to SRT significantly improved outcomes.

I discussed with my medical team the Mayo data and the emerging clinical trials. They dismissed it, saying there was not "long term data" to support it. Sadly, I listened, from my chart you can see Mayo was right as were the emerging clinical trials combining short term ADT with the SRT. That was the last time I let my medical team make the treatment decision, from that point forward we made joint decision based on their recommendations, my homework and treatment preference, in this case, aggressive.

You ask what level of concern, that's hard to answer, given that the word cancer strikes fear into many of us, in a way, you should be "concerned." But only in the sense that work lies ahead of you to inform yourself, gather clinical data and then in concert with your medical team, make the best possible treatment decision.

You may be in a "curative" stage where informed by the imaging and other clinical data such as PSA doubling and velocity, location(s) of the PCa, doublet or triplet therapy may either cure you or provide a durable and long term progression free survival.

The changes in knowledge, imaging and treatment options over the last 5-10 years has been exponential, opening up the possibilities of either a cure or managing this damn cancer as a "chronic" disease, say, like diabetes or AIDS.

One think to think about is changing your horizon for deciding on treatment. Depending on your life expectancy, your medical team may think in 10, 15, 20 year periods...I say, ask, will this provide progression free survival for the next 3-5 years, if so, we can expect new treatments to emerge.

So, do not hit the panic button, I know, don't 27K men a year die from PCa, yes, but how many are living with it and for how long? I have pretty aggressive PCA, coming up on nine years since my diagnosis and first treatment.

I believe you are doing the right thing, having a 2nd PSA, if that shows another increase, image, then informed by clinical data, homework, and your medical team, make a decision about whether to treat, when, with what, how long, what criteria do we use to come off the treatment (anyone on your medical team start talking about lifetime of ADT, fire them!).

Kevin