Several tests are used to diagnose prostate cancer

Digital rectal examination (DRE): In a DRE, the physician inserts a lubricated, gloved finger into the rectum to feel the surface of the prostate gland. Healthy prostate tissue is soft, like the fleshy tissue of the hand where the thumb joins the palm. Malignant tissue is firm, hard, and often asymmetrical or stony, like the bridge of the nose. However, as many as one-third of patients diagnosed with prostate cancer have a normal DRE.

The physician "stages" the tumor based on its size, the character of its cells, and the extent of metastasis. TBM staging is considered standard. Prostate cancer staging is the process by which physicians categorize the risk of cancer having spread beyond the prostate, or equivalently, the probability of being cured with local therapies such as surgery or radiation. Once patients are placed in prognostic categories, this information can contribute to the selection of an optimal approach to treatment. The information considered in such a prognostic classification can be based on physical examination, imaging studies and blood tests (so-called "clinical stage"), or based on the extent of disease as revealed in a surgical specimen (so-called "pathologic stage").

There are two schemes commonly used to stage prostate cancer. The most common is promulgated by the American Joint Committee on Cancer, and is known as the TNM system, which evaluates the size of the tumor, the extent of involved lymph nodes, and any metastasis (distant spread) and also takes into account cancer grade. As with many other cancers, these are often grouped into four stages (I‐IV). Another scheme, now used less commonly for research, but often still used by clinicians, is the Whitmore-Jewett stage.

Briefly, Stage I disease is cancer that is found incidentally in a small part of the sample when prostate tissue was removed for other reasons, such as benign prostatic hypertrophy, and the cells closely resemble normal cells and the gland feels normal to the examining finger. In Stage II more of the prostate is involved and a lump can be felt within the gland. In Stage III, the tumor has spread through the prostatic capsule and the lump can be felt on the surface of the gland. In Stage IV disease, the tumor has invaded nearby structures, or has spread to lymph nodes or other organs. Grading is based on cellular content and tissue architecture from biopsies (Gleason) which provides an estimate of the destructive potential and ultimate prognosis of the disease.

TNM Staging

Evaluation of the (primary) tumor ('T')
TX: cannot evaluate the primary tumor
T0: no evidence of tumor
T1: tumor present, but not detectable clinically or with imaging
T1a: tumor was incidentally found in less than 5% of prostate tissue resected (for other reasons)
T1b: tumor was incidentally found in greater than 5% of prostate tissue resected
T1c: tumor was found in a needle biopsy performed due to an elevated serum PSA
T2: the tumor can be felt (palpated) on examination, but has not spread outside the prostate
T2a: the tumor is in half or less than half of one of the prostate gland's two lobes
T2b: the tumor is in more than half of one lobe, but not both
T2c: the tumor is in both lobes
T3: the tumor has spread through the prostatic capsule (if it is only part-way through, it is still T2)
T3a: the tumor has spread through the capsule on one or both sides
T3b: the tumor has invaded one or both seminal vesicles
T4: the tumor has invaded other nearby structures
It should be stressed that the designation "T2c" implies a tumor which is palpable in both lobes of the prostate.
Tumors which are found to be bilateral on biopsy only but which are not palpable bilaterally should not be staged as T2c.

Evaluation of the regional lymph nodes ('N')
NX: cannot evaluate the regional lymph nodes
N0: there has been no spread to the regional lymph nodes
N1: there has been spread to the regional lymph nodes

Evaluation of distant metastasis ('M')
MX: cannot evaluate distant metastasis
M0: there is no distant metastasis
M1: there is distant metastasis
M1a: the cancer has spread to lymph nodes beyond the regional ones
M1b: the cancer has spread to bone
M1c: the cancer has spread to other sites (regardless of bone involvement)

Evaluation of the histologic grade ('G')
Usually, the grade of the cancer (how different the tissue is from normal tissue) is evaluated separately from the stage; however, for prostate cancer, grade information is used in conjunction with TNM status to group cases into four overall stages.
GX: cannot assess grade
G1: the tumor closely resembles normal tissue (Gleason 2–4)
G2: the tumor somewhat resembles normal tissue (Gleason 5–6)
G3–4: the tumor resembles normal tissue barely or not at all (Gleason 7–10)
Of note, this system of describing tumors as "well-", "moderately-", and "poorly-" differentiated based on Gleason score of 2-4, 5-6, and 7-10, respectively, persists in SEER and other databases but is generally outdated. In recent years pathologists rarely assign a tumor a grade less than 3, particularly in biopsy tissue. A more contemporary consideration of Gleason grade is:
Gleason 3+3: tumor is low grade (favorable prognosis)
Gleason 3+4 / 3+5: tumor is mostly low grade with some high grade
Gleason 4+3 / 5+3: tumor is mostly high grade with some low grade
Gleason 4+4 / 4+5 / 5+4 / 5+5: tumor is all high grade

Overall Staging
The tumor, lymph node, metastasis, and grade status can be combined into four stages of worsening severity.

Whitmore-Jewett staging

The Whitmore-Jewett system is similar to the TNM system, with approximately equivalent stages. Roman numerals are sometimes used instead of Latin letters for the overall stages (for example, Stage I for Stage A, Stage II for Stage B, and so on).

A: tumor is present, but not detectable clinically; found incidentally
A1: tissue resembles normal cells; found in a few chips from one lobe
A2: more extensive involvement
B: the tumor can be felt on physical examination but has not spread outside the prostatic capsule
BIN: the tumor can be felt, it does not occupy a whole lobe, and is surrounded by normal tissue
B1: the tumor can be felt and it does not occupy a whole lobe
B2: the tumor can be felt and it occupies a whole lobe or both lobes
C: the tumor has extended through the capsule
C1: the tumor has extended through the capsule but does not involve the seminal vesicles
C2: the tumor involves the seminal vesicles
D: the tumor has spread to other organs