Intended for healthcare professionals

Rapid response to:

Press Press

The PSA storm

BMJ 2002; 324 doi: https://doi.org/10.1136/bmj.324.7334.431 (Published 16 February 2002) Cite this as: BMJ 2002;324:431

Rapid Response:

PSA screening - what is the NNT (number needed to test)?

I was surprised to find no mention in the debates on PSA screening of
how many men need to be tested (NNT) to identify one prostate cancer or
prevent one related death. I believe that an agreed upon estimated NNT
(or range of NNTs) should be the first step to address this controversy.

For every 1000 men age 55-74 who undergo initial PSA screening and
digital rectal examination, 189 would have PSA greater than 4 ng/mL and 27
of whom would have biopsy-proven prostate cancer.(1,2) If we exclude
patients with minimal disease who require no treatment and those with
incurable advanced disease, there are left 14 patients (50%)(3-5) with
potentially curable, localised disease. About 10 of these patients (70%)
would be cured with prostatectomy(6-8) or radiation,(9-12) assuming cure
as being alive and disease-free 10 years after treatment.

In other words, PSA screening could prevent 10 prostate cancer-
related deaths per 1000 men tested, or an NNT of 100. Whether this NNT is
too high or too low depends on many other factors, such as the risks
associated with PSA testing. However, I suspect that many involved in
this debate have very different NNTs in mind, and hence their apparently
irreconcilable differences.

1. Mettlin C, Murphy GP, Ray P, et al. American Cancer Society--
National Prostate Cancer Detection Project. Results from multiple
examinations using transrectal ultrasound, digital rectal examination, and
prostate specific antigen. Cancer 1993;71(3 Suppl):891-8.

2. Schroder FH. The European Screening Study for Prostate Cancer. Can
J Oncol 1994;4(Suppl 1):102-5; discussion 6-9.

3. Epstein JI, Walsh PC, Carmichael M, et al. Pathologic and clinical
findings to predict tumor extent of nonpalpable (stage T1c) prostate
cancer. JAMA 1994;271(5):368-74.

4. Polascik TJ, Oesterling JE, Partin AW. Prostate specific antigen:
a decade of discovery--what we have learned and where we are going. J Urol
1999;162(2):293-306.

5. Tumor Characteristics of Prostate Cancer Patients. National Cancer
Data Base (NCDB). 1995. Available from
http://www.fac.org/dept/cancer/ncdb/prostat3.html. Accessed 31 August,
2001.

6. Trapasso JG, deKernion JB, Smith RB, et al. The incidence and
significance of detectable levels of serum prostate specific antigen after
radical prostatectomy. J Urol 1994;152(5 Pt 2):1821-5.

7. Zincke H, Oesterling JE, Blute ML, et al. Long-term (15 years)
results after radical prostatectomy for clinically localized (stage T2c or
lower) prostate cancer. J Urol 1994;152(5 Pt 2):1850-7.

8. Pound CR, Partin AW, Epstein JI, et al. Prostate-specific antigen
after anatomic radical retropubic prostatectomy. Patterns of recurrence
and cancer control. Urol Clin North Am 1997;24(2):395-406.

9. Bagshaw MA, Cox RS, Ray GR. Status of radiation treatment of
prostate cancer at Stanford University. NCI Monogr 1988(7):47-60.

10. Zagars GK, von Eschenbach AC, Johnson DE, et al. The role of
radiation therapy in stages A2 and B adenocarcinoma of the prostate. Int J
Radiat Oncol Biol Phys 1988;14(4):701-9.

11. Perez CA, Lee HK, Georgiou A, et al. Technical and tumor-related
factors affecting outcome of definitive irradiation for localized
carcinoma of the prostate. Int J Radiat Oncol Biol Phys 1993;26(4):581-91.

12. Hanks GE, Krall JM, Hanlon AL, et al. Patterns of Care and RTOG
studies in prostate cancer: long-term survival, hazard rate observations,
and possibilities of cure. Int J Radiat Oncol Biol Phys 1994;28(1):39-45.

Competing interests: No competing interests

23 February 2002
Mario L. de Lemos
Provincial Drug Information Coordinator
British Columbia Cancer Agency, Vancouver, British Columbia, V5Z 4E6