Early detection of prostate cancer. Serendipity strikes again
M. McNaughton Collins, D. F. Ransohoff and M. J. Barry
General Medicine Division, Medical Services, Massachusetts General Hospital, Boston 02114, USA.
An underappreciated characteristic of prostate cancer screening is that it
may detect some prostate cancers solely by serendipity or chance.
Serendipity, previously described in the detection of colonic neoplasms,
could affect prostate cancer detection when a screening test result is
abnormal for reasons other than the presence of prostate cancer, but
prostate cancer is coincidentally detected during the subsequent evaluation
of the abnormal screening result. We reviewed published articles about
prostate cancer screening, searching for evidence of serendipity. We
defined serendipity in digital rectal examination (DRE) screening as the
discovery of a prostate cancer by the random biopsy of an area of the
prostate gland other than the palpable suspicious area that prompted the
biopsy. We defined serendipity in prostate-specific antigen (PSA) screening
as the discovery of a prostate cancer by the random biopsy of a nonpalpable
(stage T1c) prostate cancer less than 1.0 cm3 in volume, since tumors less
than 1.0 cm3 are generally too small to cause elevated PSA levels. We found
that serendipity may be responsible for the detection of more than one
quarter of apparently DRE-detected prostate cancers and up to one quarter
of apparently PSA-detected cancers. Additionally, serendipity played a
larger role in the detection of smaller tumors that are common but of
uncertain clinical significance. We conclude that serendipity-detected
prostate cancers contribute to an overestimation of the true information
value of DRE and PSA screening. Whether serendipity is advantageous in
prostate cancer screening depends on the as yet uncertain outcomes for men
with smaller prostate cancers. However, given our estimates of the
potential magnitude of the impact of serendipity, the currently popular
DRE- and PSA-based screening strategy may not be optimal. If smaller
prostate cancers are important, then we are not finding enough; if they are
unimportant, then we are finding too many that we may feel compelled to
treat aggressively.
