PSA and cancer staging

In spite of the considerable overlap in serum PSA between stages of prostate cancer

• PSA alone correlates reasonably well with pathological, and to a lesser extent, clinical CAP staging

• There is a direct relationship between tumor volume and serum PSA

Normograms (e.g., Partin's table) seek to enhance the predictive power of PSA by combining PSA with clinical stage and the his-tological (Gleason) grade in predicting the final pathological stage. These are now being used increasingly to direct patient management. As a general rule, the majority of men (80%) with CAP and a PSA of <4 ng/mL will have organ-confined disease on final analysis. The proportion of patients with extra-prostatic disease increases with a rising serum PSA level, with roughly 65% and <50% of patients having organ-confined disease with a PSA of 4-10 ng/mL and >10 ng/mL, respectively.

Lymph node metastases: multivariate analysis has demonstrated that PSA is the best predictor of the possibility of lymph node metastases, though its predictive ability is significantly enhanced if combined with clinical stage and Gleason grade. Nodal disease is—

• Found in 20% of those with a PSA of >20 ng/mL

• Found in over 75% of patients with PSA >50 ng/mL

It is argued that use of predictive tables can significantly reduce the number of unnecessary lymph node sampling.

Skeletal metastases: PSA has also been shown to be the best individual predictor of results of a bone scan in patients with CAP. There is little justification in routinely performing bone scans in asymptomatic patients with a PSA <10 ng/mL, since the presence of skeletal metastases, based on a positive bone scan, is rare. The majority of patients with a significantly elevated PSA (>50 ng/mL) will have a positive bone scan.

• PSA has revolutionized detection and management CAP

• PSA remains the single most useful tumor marker compared to other cancers markers

• PSA shows good correlation with tumor stage, lymph node status, and likelihood of skeletal metastases

• Improvement in immunoassay detection techniques and modifications in the use of other molecular forms of PSA (e.g., free and complex PSA) may improve diagnostic accuracy

■ Limited specificity and sensitivity

■ PSA affected by age, BPH, infection, lower urinary tract manipulation

■ Widespread screening will inevitably result in over-investigation or over-treatment in a small proportion of patients

(b) ELECTROLYTES

Overview

• Electrolyte ions are critical for a variety of cellular reactions, including nerve impulse conduction and water balance

• Electrolyte imbalances may occur in virtually any urological pathological process

• Indications for electrolyte estimation are many and varied, and can be justified for almost any urological condition including—

■ Existing or risk of renal failure

■ In patients taking certain medications (e.g., diuretics, digoxin)

■ Existing or risk of dehydration or malnutrition

■ Urinary stone disease

■ Organ failure (e.g., cardiac, liver, pulmonary failure) Interpretation

Some urologically important causes of electrolyte disturbances are highlighted below (Table 2.3).

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