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Breast cancer is the most common cancer among women in India and a large part of the world. In India, it has overtaken cervical cancer, which was, for many years, the most common cancer among Indian women. It is, therefore, natural to wonder why otherwise healthy women fall prey to breast cancer.
To understand this, it is important to understand what causes a cell to become cancerous. Each cell of the body contains DNA which carries genes that regulate all its functions, including its growth. Damage to a gene is called a mutation and may result uncontrolled growth and other changes that allow the damaged cell to move out of its normal location and develop an ability to grow in other parts of the body. Factors that increase the risk of a mutation, therefore increase the risk of cancer.
Breast cancer occurs primarily because of mutations triggered by the female hormone, estrogen. A large number of mutations are detected by the body and are never able to convert a normal cell into a cancer cell. Some may, however, escape this surveillance by the body’s immune system and turn into cancer cells.
It is natural, then, that situations that result in an increased or decreased exposure to estrogen, result in increased or decreased risk of cancer-causing mutations. Estrogen is produced in large quantities in the beginning of each menstrual cycle. Estrogen exposure, therefore, increases in women in whom menstrual periods start early or menopause occurs late. This, in turn, increases the risk of breast cancer.
Since the menstrual cycle is interrupted in women who are pregnant or breastfeeding, these reduce estrogen exposure, and are protective. A woman who is otherwise healthy, but has not been pregnant, are therefore at a higher risk of having breast cancer compared to a woman who has given birth. This also holds true for a woman’s age at first full-term pregnancy; an earlier age results in an earlier interruption in exposure to estrogen and has a protective effect. Having several children and breastfeeding them, also has a protective effect, reducing the risk of breast cancer.
Interestingly, besides the ovaries, estrogen is also produced by fat cells. This becomes relevant in women in whom menopause has occurred and estrogen is not being produced by the ovaries. Overweight and obese women, therefore, have higher estrogen levels following menopause compared to women with normal body weight. This increases their risk of developing breast cancer.
Alcohol increases estrogen levels in the body and regular intake of alcohol leads to an increased risk of developing cancer in an otherwise healthy person. This is partially related to the estrogen pathway and may also happen unrelated to estrogen.
In addition to the above, some women may inherently be susceptible to cancer due an abnormality in their genetic makeup. The most common among these is abnormalities in BRCA 1 and 2 genes. The normal function of these genes is to repair damaged DNA. An apparently healthy person may carry a mutations in either gene, usually inherited, which increases susceptibility to certain cancers, mostly those of the breast and ovary. In addition, mutations of other genes, such as TP53, PTEN, CDH1, ATM, CHEK2, or PALB2, also lead to a higher risk of breast cancer. Such hereditary cancers are about 5-10 percent of all breast cancers in India.
In conclusion, some causes of breast cancer are modifiable. Lifestyle habits can reduce breast cancer risk sometimes. Post-menopausal women who maintain normal body weight and an exercise regime are on the top of this list. Restricting or avoiding regular alcohol intake is another. Some risk factors are subject to social norms, personal choice and constraints, such as the time of first childbirth, number of children and breastfeeding. Some are, however, non-modifiable, such as an inherited risk.
The outcomes of breast cancer treatment have improved significantly over the last few years, due to advances in screening, investigation and treatment. Undergoing regular breast cancer screening based on one’s age and risk profile should therefore necessarily be a part of a woman’s self care regime.