Genetic predisposition is the commonest risk factor for breast cancer development

I usually meet relatives for some of my patients and I'm frequently asked questions about the of breast cancer.

Dr Joseph Kamugisha

I usually meet relatives for some of my patients and frequently asked questions about the of breast cancer.

Breast cancer is the most prevalent cancer in the country with the highest genetic predisposition.

Based on available information, there is proven evidence that inherited breast cancer genes appear directly responsible for 5 per cent to 10 per cent of all breast cancers.

Although much remains to be discovered about the heritable factors involved, enormous strides have been made in understanding inherited susceptibility to breast cancer.

These advances are based on the discovery and characterisation of a number of genes responsible for the clustering of breast cancer in certain families. There is still a lot of information to avail as regards genetic influence in breast cancer development.

Hard core sciences like gene to gene or gene to environment interactions that modulate the risk of breast cancer development still have to be studied and little information is known.

Given the strong influence of molecular genetics, there is a tendency to assume that familial clustering of disease invariably results from inherited predisposition.

Other intriguing question marks over genetic influence in breast cancer development have been on surface. For example, geographically limited environmental exposure to carcinogens, which might affect an extended family living in close proximity is something to think about.

Other conditions to be studied are culturally motivated behaviour that alters risk factor profile such as age at first live birth and socioeconomic influences that might result in differing dietary exposures.

In addition, multiple complex inherited genetic factors likely influence the extent to which a risk factor for breast cancer plays a role in any one individual; such modifying effects are likely to be shared among genetically related members of an extended family.

Breast cancers caused by mutations in high-penetrance susceptibility genes have several distinctive clinical features. Age at diagnosis is considerably younger than in sporadic cases, the prevalence of bilateral breast cancer is higher, and associated tumours are noted in some families.

Associated tumours may include ovarian, colon, prostate, pancreatic, endometrial cancers, breast cancer in male family members and sarcomas.

We understand from the clinical perspective that tumours arising in the setting of inherited mutations in susceptibility genes have different characteristics with regard to grade, estrogen receptor status, and molecular profile of the disease.

Whether these cancers respond differently to treatment or are associated with a worse prognosis than sporadic tumours remains controversial. This controversy has made us think twice or development recurrent worries in regard to the situation of our patients.

 Hereditary breast cancer is commonly caused by inherited mutations like the BRCA1 and BRCA2 genes.

In a healthy person with normal breast cells, these genes help prevent cancer by making proteins that keep the cells from growing abnormally. People who inherit a mutated gene from a parent have high risks to develop breast cancer in their lifetime.

BRCA1 runs in families and the risk to develop breast cancer with this mutation is as high as 80 per cent and for BRCA2 the risk is lower as compared to the mutation BRCA2.

Breast cancers linked to these mutations occur more often in younger women and more often affect both breasts, than cancers not linked to these mutations. Women with these inherited mutations also have an increased risk of developing other cancers, especially ovarian cancer.

There are other gene mutations that can also lead to inherited breast cancers but are very rare. For example, the P53 gene mutation does not usually increase the risk of breast cancer as compared to the BRCA genes.

Use of the oral contraceptives or other hormonal implants in birth control pills has been highly implicated in breast cancer development.

Contraceptive pills contain estrogen or progesterone or both hormones. They are graded as the second-highest common risk factor in breast cancer development though there is still much information to elaborate on this issue.

Researchers in breast cancer discovered that women who use oral contraceptives have an increased risk of breast cancer as compared to women who never use them. However, this risk is likely to be reversed once the oral contraceptives usage is reduced or stopped completely.

 Dr Joseph Kamugisha is an oncologist at Rwanda Military Hospital, Kanombe



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