Dr. Ajay Anand
Prostate cancer has hitherto been diagnosed on basis of raised serum markers like PSA (Prostate Specific Antigen) coupled with prostate biopsy.
PSA is a serum marker for prostate, which has been available for a long time. Normal values range from 0-4ng/ml. PSA is organ specific but not disease specific. It may be raised in various pathologies of prostate other than prostate cancer. PSA may be raised in urinary tract infection, after catheterization, prostatitis, post digital rectal examination, after prostate biopsy etc. There are various isoforms of PSA available – free and bound PSA.Sine early 1990s to till date, greater percentage of free isoform of serum PSA indicated greater likelihood that prostate pathology was benign rather than prostate cancer.
Raised values of PSA above normal limit warrant exclusion of above mentioned causes of rise of this marker. Still persistence of raised values of repeat PSA has been an indication for prostate biopsy to exclude prostate cancer.
PSA is not a good marker in two conditions:-
* Screening purposes (due to its limited specificity for clinically significant prostate cancer, resulting in unnecessary biopsies for false positive results as well as detection of some indolent tumors that would not have caused harm during the patient’s lifetime).
* Identification of high risk individuals.
Recently US FDA in 2014 based on certain clinical trials has approved a novel serum marker for prostate cancer detection – PHI (Prostate Health Index) which is calculated using the formula
* [-2]proPSA/free PSA) × ? Total PSA.
As per this formula of PHI, men with a higher total PSA and proPSA (precursor form of PSA) with a lower free PSA are more likely to have clinically significant prostate cancer.
proPSA[-2] form is commercially available in USA with improved performance over either total or free PSA for prostate cancer detection on biopsy.This proPSA[-2] form is not yet commercially available in India but is expected to become available soon.
PHI has greater specificity for distinguishing prostate cancer on biopsy compared with PSA or percentage free PSA (%fPSA).The mean PHI scores were 34 and 49 for men with negative and positive biopsies, respectively in a study by Catalona and colleagues.
Higher the value of PHI, greater is possibility of detection of prostate cancer on biopsy which may be aggressive forms of prostate cancer; and vice versa. So this is basically proPSA , which in conjuction with total PSA directly correlates with detection and aggressiveness of prostate cancer, necessitating early treatment.PHI is also consistently associated with Gleason score and upgrading during active surveillance.
PHI not only outperforms free and total PSA for prostate cancer detection, but it also improves the prediction of high-grade and clinically-significant prostate cancer.
PHI also predicts the likelihood of progression during active surveillance, providing another noninvasive modality to potentially select and monitor this group of patients.
Although no single marker in isolation has perfect performance characteristics, PHI is a simple and inexpensive blood test that should be used as part of a multivariable approach to screening. PHI should be considered as part of the standard urologic armamentarium for biopsy decisions, risk stratification and treatment selection.
(The author is presently working as Consultant Urologist in Superspeciality Hospital, GMC, Jammu).
Dr. Ajay Anand