Phi Index Can Select Patients with Prostate Cancer for Active Surveillance

April 2014, Vol 5, No 3

San Francisco, CA—A new tool called the Prostate Health Index (phi) can identify which patients with favorable-risk prostate cancer can safely be managed with active surveillance and which patients will probably require treatment. The phi index is relatively low tech and is calculated using 3 serum measurements: prostate-specific antigen (PSA), free/total PSA, and a measurement called [-2]proPSA.

A preliminary study of the phi index in the active surveillance setting showed that it provided a more accurate estimate of the course of illness than PSA or free/total PSA. The study was reported at the 2014 Genitourinary Cancers Symposium.

“This is a new method for identifying which patients assigned to watchful waiting will need treatment. There are many patients who don’t need treatment even 10 years after diagnosis,” said lead investigator Andrew Eichholz, MD, of the Institute of Cancer Research, Royal Marsden NHS Foundation Trust, Sutton, United Kingdom.

Dr Eichholz explained that phi is starting to be used in the prebiopsy setting in the United States. Although he is quite enthusiastic about the applicability of phi in the active surveillance setting, he said, “It is not ready for prime time. The phi index needs to be validated. We are the first group to study it [in this setting], and another group is also studying it. If it is validated, it could change the way we manage these patients.”

The investigators sought to determine the predictive value of phi in a retrospective study based on frozen blood samples from 370 patients collected at diagnosis a median of 11.4 years ago. The patients had stage T1/T2 cancer, Gleason scores of ?3 + 4, and a PSA of <15 ng/mL.

Patients were monitored with PSA testing every 6 months and repeat biopsy every 2 years. Treatment was indicated for patients with a PSA velocity of >1 ng/mL annually or a Gleason score of ?4 + 3 on repeat biopsy.

A total of 115 patients started treatment after a median of 11.4 years. Phi was significantly associated with the time to treatment (P <.001).

The test results were grouped into quartiles according to phi. The investigators determined that the cutoff point for phi was <31.4 for the lowest-risk quartile and >58.5 for the highest-risk quartile. Among the lowest-risk patients, the test predicted that 95% would not need therapy within 5 years from diagnosis, whereas among the highest-risk patients, 54% would require treatment within 5 years.

After 10 years, 37% of the patients still did not require treatment, and approximately 20% needed treatment within 2 years of diagnosis.

“If phi is validated in this setting, it will be a useful tool for discussions with patients,” Dr Eichholz stated.

Phi received premarketing approval from the US Food and Drug Administration in June 2012 for use in men (not diagnosed with prostate cancer) with a PSA in the range of 4 ng/mL to 10 ng/mL. At that time, a multicenter study showed that phi reduced unnecessary biopsies by 31%.

The phi assay kit is marketed by Beckman Coulter.

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