Testing genes would be a better and more
accurate method to detect aggressive prostate cancers than the conventional
methods, say researchers.
Cancer of the prostate is the leading cause of death
in older men in the world and is the third most common cause of death
from cancer in men of all ages. Prostate cancer is
one disease that takes a highly variable course. At times, it takes as long as
ten years to spread, a fact that allows doctors to watchfully wait especially
for men older than 75. At other times, the cancer takes an aggressive line
moving fast and killing the patient in a few years.
The prognosis of men with prostate cancer is assessed
using a grading system called the Gleason Grading System. The Gleason Score, as it is
referred to, is used internationally to determine the severity of the cancer.
It has acted as a decision maker that enabled physicians to choose from the
different management options for the cancer. The Gleason system is based on the
microscopic appearance of the tumor tissue. Patient's tumor tissue is scored on
the cell patterns.
A low Gleason score means the cancer is less
likely to spread and is similar to normal prostate tissue. A high score
points to a poorer prognosis. However, recent studies challenge this concept. It
has been found that a number of men with low Gleason scores develop aggressive
prostate cancers. A low score hence does not definitely mean that the cancer
will not turn hostile.
It was thus necessary to devise a new system that could predict
patients with low Gleason scores who will have poor survival. The
research that followed led scientists to genes. Study of gene expression,
using a technique called microarray analysis has let researchers to begin the
process of identifying genes which predispose to poorer outcome.
Gene screening may allow the most lethal types of
prostate cancer to be pinpointed earlier and more definitively than current
tests, said researchers. The landmark study used data from 281 patients
from Sweden who had been recruited between 1977 through 1999. Their
tumour tissues were studied for genetic expressions associated with prostate
cancer. Microarray analysis allowed the measurement of the expression of
huge numbers of genes simultaneously.
Patients from the Swedish study were classified into five prostate
cancer subtypes, each of which had a distinct
predicted outcome. Two subtypes of prostate cancer were found to carry a
3.2-fold increased risk of death. These two high-risk subtypes had a number of men with poor prognoses even though
they had low Gleason score tumors.
Gene tests could thus enable early identification of
the aggressive form of prostate cancers that current tests miss out. The authors, however, recommend larger
prospective trials to establish their findings.
Reference: Proceedings of the National
Academy of Sciences, November 28, 2011; Markert EK, Mizuno H, Vazquez A, Levin AJ. Molecular classiﬁcation of prostate cancer using curated