The A metanalysis of cohort study involving 11722 cases

The
study “Contemporary hormonal contraception and the risk of breast cancer” is a
nationwide large prospective study conducted in Denmark involving all women between
15 to 49 years to find the association of modern day hormonal contraceptives and
risk of breast cancer. In this study 1.8 million women were followed for 10.9 years.
Denmark nationwide registries provided individually updated information
of hormonal contraception, breast-cancer diagnoses, and potential confounders. The study documented 11517 cases
of breast cancer in this population during the study period.

 

  The
findings of the study are

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– 20 %
higher risk of breast cancer in women who are current or recent users of
hormonal contraception.

-Risk
increased with duration of use of hormonal contraception from 9% in females who
used for 1 year to 38 % in women who used for more than 10 years.

– All
hormonal contraception methods including progesterone only IUD showed increased
risk when compared with never users.

– The
risk persisted even after stopping hormonal contraception in patients who have
taken it for more than 5 years.

-The
absolute increase in breast cancer among current and recent hormonal
contraceptive user was 13 /100000 person’s years or one extra breast cancer for
every 7690 hormonal contraceptive users in 1 year.

The
authors concluded that hormonal contraceptives are associated with increased
risk of breast cancer but the absolute increase in risk is small.

Comment:

Why the
study is important?

Hormonal
contraception (pills, hormonal IUD, injections) is reliable form of
contraception with less failure rates.  Cancer
risk remains a concern with long term use of hormonal contraception.  To answer this, a large cohort study reported
a significant lower rates of large bowel, uterine body and ovarian cancers, and
increasing risk trends towards cervical and CNS tumors with long term hormonal
contraceptive users. Incidence of
breast cancer was similar in pill users and never users in that study. (2) A metanalysis of cohort study involving 11722 cases and over
850000 women reported non-significant increase in breast cancer in ever users
of oral contraceptives compared with non users (RR1.08 CI 0.99-1.17) .(3) A recent study from
Thailand showed that oral contraceptives might increase risk of
breast cancer.(4) There is no data on
modern day hormonal contraception which were considered safer options in
regards to cancer risk. The study was conducted to answer if current hormonal
formulations increased risk of breast cancer.

What are the messages from the study?

The present study gains importance by adding
significant data on current hormonal contraceptives including low estrogen
pills, progesterone only pills and their breast cancer risk for which evidence
was lacking and one can conclude that no present day formulation of hormonal
contraception is free of breast cancer risk . 

Secondly the persistent risk in woman who used
hormonal contraception for more than 5 years is also an additional input to
existing data. 

Lastly the study showed how a large informative
research is possible in relatively low cost to address common but important
questions when nationwide registries for medicines, cancer are maintained and
are linked with each other.

Critical review:

            Limitations of study include factors
like age at menarche, breast feeding, alcohol consumption or physical activity,
environmental and dietary factors was not adjusted. The absolute risk of breast cancer will be determined by the
woman’s individual baseline risk which includes above factors. Authors
explained decrease in incidence of breast cancer in patients who stopped
hormonal contraception within 5 years is not expected if these risk factors
acted as confounders. Weather these factors influence risk in long term users
is unknown. Marsden  reported that excess risk  associated with hormonal contraceptive is
small and comparable with risk by other modifiable risk factors like smoking,
alcohol consumption , age at first birth etc. for hormone sensitive breast
cancer in premenopausal women.(5)

    Though there
is increased risk in breast cancer, there is no evidence till date that
contraceptive use leads to increased breast cancer specific mortality when
compared with never users.   Contraceptive
users tend to be more health conscious and likely to seek medical attention early
when they have breast symptoms can lead to many early breast cancer diagnosis
in this group theoretically.   Weather this increased risk is associated with
advanced disease stage or increased disease specific mortality in contraceptive
users’ needs to be answered.

Implications in Indian scenario:

In
India the incidence of breast cancer is 25.8 per 100000. The data of National
Family Health Survey 4 have shown only 53.5 % of population use some of contraception.  Unlike Denmark where 39% woman in
reproductive age group uses hormonal contraception, only 4.1% in India use
hormonal pills.  (6).The population at risk of breast
cancer due to oral contraception in our country is smaller when compared to western
world. The  advantages of
contraception  such as good efficacy in
avoiding unwanted pregnancy , reduced risk of certain malignancy like
colorectal , endometrial should also be considered before counseling the
patient regarding contraception . UK Medical Eligibility criteria (UKMEC) recommendations are based on
evidence and consensus opinion, which assists clinicians in prescribing safe
and suitable contraception .It recommends considering the individual absolute
risk in women with high risk before advising contraception.

  

            In conclusion clinicians should use the data of the study to discuss
the advantages and disadvantages of hormonal and nonhormonal contraceptive
methods (condom, diaphragm, copper IUD) and help women to take informed
decision on contraceptive method most consistent with her lifestyle with
minimal side effects.