Prostate Cancer (cont.)
How are Prostate Cancer Stages Defined?
The primary staging assessment of prostate cancer is usually made by digital rectal examination (DRE), prostate specific antigen (PSA) measurement, and bone scan, supplemented with computed tomography (CT) or magnetic resonance imaging (MRI) and chest X-ray in specific situations.
Staging is a system of classifying tumors by size, location, and extent of spread, local and remote.
Staging is an important part of treatment planning because tumors respond best to different treatments at different stages.
Stage is also a good indicator of prognosis, or the chances of success after treatment.
Clinical staging provides the initial information about the extent of disease that is used to plan therapy. However, clinical staging can underestimate the extent of the tumor, when compared with results based upon pathologic examination of a resection specimen (pathological staging).
Conventional stages of prostate cancer are as follows:
- Stage I (or A): The cancer cannot be felt on digital rectal exam, and there is no evidence that it has spread outside the prostate. These are often found incidentally during surgery for an enlarged prostate.
- Stage II (or B): The tumor is larger than a stage I and can be felt on digital rectal exam. There is no evidence that the cancer has spread outside the prostate. These are usually found on biopsy when a man has an elevated PSA level.
- Stage III (or C): The cancer has invaded other tissues neighboring the prostate.
- Stage IV (or D): The cancer has spread to lymph nodes or to other organs.
Tumor, node, and metastases (TNM) staging:
Most urologists currently use the 2010 TNM (Tumor, Node, Metastases) staging system for prostate cancer. This is based on a combination of three criteria: the extent of the primary tumor (T stage), involvement of lymph nodes by the cancer (N stage), and the presence or absence of spread to distant areas of the body in the form of metastasis (M stage). The TNM 2010 staging system is as follows:
T-staging refers to the size of the tumor and whether it has invaded nearby tissue.
- The first level is the assessment of local tumor stage, where the distinction between intracapsular (T1 to T2) and extraprostatic (T3 to T4) disease has the most profound impact on treatment decisions.
- DRE often underestimates the tumor extension. Two-dimensional or three-dimensional ultrasound can be used to assess T-staging.
- Seminal vesicle biopsies may be used to increase the accuracy of preoperative staging in specific cases.
N-staging refers to the presence of lymph node metastases.
- Assessment should be performed only when the findings will directly influence a treatment decision.
- Current research results indicate that CT and MRI perform similarly in the detection of pelvic lymph node metastases.
- The gold standard for N-staging is operative lymphadenectomy, either by open or laparoscopic technique.
- This is usually achieved through pelvic lymph node dissection (PLND) which is a surgical procedure performed during radical prostatectomy (see section on surgical treatment). The procedure can sometimes be done through laparoscopy as a separate procedure.
- Lymphatic mapping with sentinel lymph node (SLN) biopsy is being studied as an alternative to pelvic LND in men with newly diagnosed prostate cancer. SLN evaluation has the potential to accurately identify patients with node-positive disease, while reducing the extent of surgery.
M-staging refers to the assessment of distant metastases.
- As discussed earlier, prostate cancer usually metastasizes to bone. Consequently, radionuclide bone scan, axial skeleton MRI, and PET have all been used to detect evidence of bone metastases.
- Radionuclide bone scan is the standard test for evaluation of bone metastases; however, it is not offered systematically to all patients. For example, some centers do not offer it to patients with a clinical T2 or lower, a combined Gleason score <6 and a serum PSA <10 ng/mL.
- Axial skeleton MRI is usually used to confirm the possibility of distant disease after a positive or equivocal bone scan. It has not yet replaced the scan as a primary test.
- Positron emission tomography (PET) has limited utility in clinically localized prostate cancer. Cellular uptake of the most commonly used radiotracer (18-F-fluorodeoxyglucose, FDG) is highly variable.
What is Evaluation of the Primary Tumor?
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: The tumor was incidentally found in less than 5% of prostate tissue resected (for other reasons).
- T1b: The tumor was incidentally found in greater than 5% of prostate tissue resected.
- T1c: The 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 are not palpable bilaterally should not be staged as T2c.
Evaluation of the regional lymph nodes ("N"):
- NX: The regional lymph nodes cannot be evaluated.
- 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: A distant metastasis cannot be evaluated.
- 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).
Medically Reviewed by a Doctor on 11/22/2016
Pierre-Alain Hueber, MD, PhD
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