34 AACR Cancer Progress Report 2013
production of estrogen have proven very successful at reducing
tumor recurrence if taken for five years (96-98) (see Table
6, p. 28). Moreover, recent data from long-term clinical trials
indicate that 10 years of therapy with one of these drugs,
tamoxifen (Nolvadex), is even more effective at reducing tumor
recurrence (99, 100). As all anti-estrogen drugs have serious
side effects, our knowledge that these drugs are ineffective
for women whose breast cancers are not fueled by estrogen
spares these patients from unnecessary and potentially harmful
Recent research has identified a potential new way to target
treatment that reduces tumor recurrence to only those cancer
survivors likely to benefit (101). Prior research had indicated
that regular aspirin use could lower risk of both primary and
recurrent colorectal cancer (102, 103). However, widespread
aspirin use was not recommended because of concerns over
side effects such as gastrointestinal bleeding. Fortunately,
researchers have been able to narrow down the population
of colorectal cancer survivors who will benefit from aspirin
(101). They found that regular aspirin use by colorectal cancer
survivors with tumors harboring mutations in the PIK3CA gene
reduced their risk of colorectal cancer death by about 80
percent, but that aspirin showed no benefit for survivors who
lacked this mutation in their tumors.
This knowledge promises to reduce colorectal cancer morbidity
and mortality for certain colorectal cancer survivors and to
eliminate the needless treatment of those who will not benefit.
However, additional, large-scale studies are needed before
aspirin use can become a standard treatment for patients with
PIK3CA-mutated colorectal tumors.
Despite these successes, the use of medical interventions to
reduce primary and recurrent tumor risk is not widespread.
Therefore, continued research is needed to develop more
concrete evidence to identify the most at-risk patients, better
screening approaches, and more and better ways to intervene
earlier in the progression of cancer.