Good question!  I'm not sure I've seen it explained here.

There are two staging methods:  The Whitmore-Jewett staging classification
and TNM (tumor, nodes, metastases).  The latter was developed by the
American Joint Committee on Cancer and the International Union Against
Cancer.  I have very rarely seen anyone express their stage in the older
Whitmore-Jewett classification.

So, the TNM classifies the state of one's cancer as it affects tumor (in the
prostate), lymph nodes and remote metastases.  My T (not to be confused with
testosterone) was originally diagnosed, actually predicted, to be 2c which
merely means it involved both lobes but was not expected to be outside the
prostate.  My N (lymph nodes) were obviously predicted to be 0 (zero), i.e.,
no involvement.  Furthermore, I was not expected to have remote metastases,
ergo, my M was also 0.

When they drilled into my belly, plucked my prostate and sliced and diced
it, they also grabbed a lymph sampling.  They found that the cancer had
actually extended through the prostate capsule, which would have been a 3.
If it had just done so, it would have been a 3a.  If it had done so
bilaterally, it would have been a 3b.  But, it was found in my seminal
vesicles, which is a 3c.  However, nothing was found in my lymph notes and
there was no indication of remote metastases.  So, T=3c, N=0, and M=0
(T3cN0M0).

N1 is a met in a single lymph node.  If I had one, I would be T3cN1M0.  N2
is a met between 2 cm and 5 cm.  N3 is bigger.  M1 is distant mets.  M1a is
nonregional lymph nodes.  M1b mets in bones.  M1c is mets in other sites.

I don't remember your post op biopsy report, but with the numbers you went
in with, I suspect you were Maybe a T1bN0M0.  It'll be on your doctor's
report if you don't have a copy.