However, as the tumor grows, it tends to be overrun by more malignant, poorly differentiated cancer cells that have a higher Gleason score. These poorly differentiated cancer cells are different from normal prostate cells, and as a consequence, they make less PSA. In fact, these cancer cells elevate PSA less per gram of tissue than well-differentiated cancer cells--which means that as cancers grow, the PSA level doesn't go up in a directly corresponding way. That'w why PSA levels can be normal even when cancer has spread to the seminal vesicles or pelvic lymph nodes, or it can be higher than expected in men with cancer that's confiineed to the prostate. PSA levels do not accurately estimate the growth of cancer. Thus, the true meaning of a PSA level can't be interpreted without knowing the Gleason Score. [Italics added by Walsh for emphasis.]
There is no such thing as zero PSA in a living, breathing man. Most men without a prostate, however, have very low levels of PSA, and in some cases they have such a low level that it is below the most sensitive PSA test's lower detection limit (LDL). The "ultra-sensitive" PSA test has a LDL of 0.01ng/mL (some lesser used ultra-sensitive PSA tests have an even lower LDL). So, <0.01 ng/mL is the test result for an ultra-sensitive PSA test which was below the lower detection limit. The "standard" PSA test, on the other hand, has a LDL of 0.1 ng/mL.There are sources in the body besides the prostate which produce low levels of PSA, including neurovascular bundles. These sometimes produce small amounts of PSA right around the ultra-sensitive test lower detection limits, so sometimes the results jump around a little right around that low level simply because of the natural variation of the small amounts produced. Of course, if there are remaining cancer cells, they too will produce amounts of PSA which will increase over time.The notion of "zero PSA" is somewhat of a misnomer which sometimes causes anxiety in men until they learn these facts. Low levels might be considered by some to be essentially "zero", or functionally "zero", but the threshold in one person's opinion might be different than the threshold in another person's opinion. Your example is very illustrative: is "zero" less than 0.01? less than 0.05, which is what you had heard? (this was in reference to an earlier poster's question about "what is 'zero PSA?'"; but, the point is that if you ask 3 different people (non-medical professionals) their "opinion" on the term "zero PSA" you are likely to get 3 different answers) less than 0.1? It can be a confusing term, and you won't likely hear a medical professional or an informed layperson tell you that you have "zero PSA." The best possible result is "undetectable."