Prostate Cancer Staging Update

The standard staging manual for prostate cancer is a consensus issued by the American Joint Committee on Cancer (AJCC). They have now issued the 8^th edition (at this link), which will become effective beginning January 2018. For the most part, it is consistent with the 7^th edition.

How is it used?

Staging refers to where the cancer is located in relation to the organ of origin. The purpose is to create a standard for staging that is used universally. Because universal use is important, AJCC excludes staging techniques that are not accessible everywhere – it must be available to large university teaching hospitals as well as to doctors in individual community practice. This means that such sophisticated diagnostic tools as multiparametric MRIs and advanced PET scans are excluded.

It is used in clinical practice to help assign patients to risk categories for treatment and prognosis, and it is used in clinical trials for similar purposes. Standardization is critical – every doctor reviewing the charts of patients understands that the AJCC stage means exactly the same thing. AJCC also wants to keep staging categories fairly consistent across different kinds of cancers (e.g., stage T2 means organ-contained for every cancer). Because inter-comparability over time and across cancers is an important part of its use, it is conservative – it doesn’t change all that much from edition to edition.

AJCC staging is one of several decisive parameters used for risk stratification (see below) and for determining probability of recurrence using nomograms. In the US, most of the risk stratification systems, including NCCN and CAPRA and the MSK and Han/Partin nomograms, use the AJCC system. It has been adopted in Canada, Europe and most of the rest of the world.

Clinical staging and pathological staging

AJCC distinguishes between clinical staging and pathological staging. For prostate cancer, clinical staging is determined at the time of diagnosis. Pathological staging, if it is done, is determined from the prostatectomy pathology findings. Clinical stages are usually designated by a “cT” before the number, while pathological stages are designated by a “pT” (T is German for Tier).

Clinical stages

For clinical stages, the T stage is only based on DRE findings. This represents a change from the 7^th edition, which allows for the staging based on imaging results, if reliable enough. T stage is never based on biopsy results.

Clinical extraprostatic extension (stage cT3a)
Clinical staging is cT1c or cT2a in over 95% of newly diagnosed cases. So, if stage cT2a or less is used as a cutoff, clinical T stage has low negative predictive value (i.e., a low T stage is not a good indicator of risk), but good positive predictive value (i.e., a high T stage is prognostic for recurrence after treatment). Ultrasound and MRIs are not very good at identifying small areas of extraprostatic extension. Epstein, at Johns Hopkins, has identified cancer mixed with extraprostatic tissues in biopsies taken from the apex. Eastham, at MSK, has identified cancer mixed with extraprostatic tissues in biopsies taken from the base. As of the 8^th edition, such pathological evidence is not used for staging.

The clinical stages are:

T category
TX	Primary tumor cannot be assessed
T0	No evidence of primary tumor
T1	Clinically inapparent tumor that is not palpable
T1a	Tumor incidental histologic finding in 5% or less of tissue resected
T1b	Tumor incidental histologic finding in more than 5% of tissue resected
T1c	Tumor identified by needle biopsy found in one or both sides, but not palpable
T2	Tumor is palpable and confined within prostate
T2a	Tumor involves one-half of one side or less
T2b	Tumor involves more than one-half of one side but not both sides
T2c	Tumor involves both sides
T3	Extraprostatic tumor that is not fixed or does not invade adjacent structures
T3a	Extraprostatic extension (unilateral or bilateral)
T3b	Tumor invades seminal vesicle(s)
T4	Tumor is fixed or invades adjacent structures other than seminal vesicles, such as external sphincter, rectum, bladder, levator muscles, and/or pelvic wall

Pathological stages

T category
T2	Organ confined
T3	Extraprostatic extension
T3a	Extraprostatic extension (unilateral or bilateral) or microscopic invasion of bladder neck
T3b	Tumor invades seminal vesicle(s)
T4	Tumor is fixed or invades adjacent structures other than seminal vesicles, such as external sphincter, rectum, bladder, levator muscles, and/or pelvic wall
N category
NX	Regional lymph nodes were not assessed
N0	No positive regional lymph nodes
N1	Metastases in regional lymph node(s)
M category	M criteria
M0	No distant metastasis
M1	Distant metastasis
M1a	Nonregional lymph node(s)
M1b	Bone(s)
M1c	Other site(s) with or without bone disease

Pelvic lymph node (N) staging

Pelvic lymph nodes get their own stage. They may be staged using enlarged lymph nodes on imaging (clinical staging), or based on dissection (PLND) and biopsy (pathological staging). The definition of “pelvic lymph node” includes the following groups: pelvic, hypogastric, obturator, iliac, and sacral (lateral, presacral, or promontory [ie, Gerota]). Recent studies have shown that the definition should probably be enlarged to include the common iliac nodes (see this link and this one). For the current edition, those lymph nodes are classified as M1a rather than N1.

Changes from the 7^th edition

The major changes are:

• T stage based on DRE only. Imaging is never used. (Nor is biopsy)
• Dropped the term “extracapsular” in favor of “extraprostatic.”
• No pathological T2 subcategories.

Risk stratification

AJCC has its own risk stratification system that uses the TNM staging data as well as PSA and Gleason Grade Groups. They designate their risk categories with roman numerals (e.g., IVB) and refer to them as “Prognostic Stage Groupings.” This may lead to some confusion; for example, a man with stage pT4, N0, M0, any PSA, and Grade Group 1-4 is “Stage Group IIIB,” while “Stage Group IV” refers to patients with any T stage but with N1 or M1. A patient hearing a doctor say, “You are stage four,” may be curable or incurable, depending on whether the four is the Arabic numeral (4) or the Roman numeral (IV). Fortunately, the most common risk stratification system in the US is the NCCN, which uses the designations “low risk,” “intermediate risk” or “high risk,” with sub-categories for each. Risk stratification systems may include many other risk factors beyond stage, grade and PSA. It is a complex topic which will be dealt with at a later time.

Judgment

While there are very good reasons for the staging rules established by AJCC, they do not replace judgment. MRIs, PET scans, genetic data, and detailed biopsy findings, while not part of the AJCC system, should not be ignored if available. The clinician seeing a moderate bulge on an MRI that he could not feel on a DRE is justified in treating the patient as if he has extraprostatic extension, and possibly recommending against surgery and for brachy boost radiation. AJCC staging is an aid to judgment, not a replacement for judgment.