Why does cancer not affect the heart?
S. RAJA SUDHARSAN
Tiruchirappailli, Tamil Nadu
Heart cancers do occur, albeit rarely. Cancer is in an abnormal, uncontrolled proliferation of cells, usually fatal. In general, tumours may be malignant (cancerous) or benign. The former is rapidly fatal if untreated while the latter causes relatively little harm.
Cancer in any organ can be primary, originating in that organ itself, or secondary, when it has spread from some other site. Secondary is either direct when it spreads by contiguity or indirect when the spread is through lymphatics or blood.
Thus heart cancer (primary cardiac tumour) is cancer that arises in the heart. Cancerous tumours that begin in the heart are more often sarcomas, a type of cancer that originates in the soft tissues of the body.
The vast majority of heart tumours are benign (non-cancerous); they include myxomas, myomas, fibromas, rhabdomyomas hamartomas.
Although still rare, most cancers found in the heart are secondary; having come from elsewhere in the body. These include lymphomas that originate in the chest near the heart and spread by contiguity — direct. Other cancers that spread to the heart include melanomas (tumours arising in black pigment forming cells) and sarcomas — indirect spread.
The general belief is that cells that divide regularly (tissues that are constantly regenerating such as the skin, intestines, etc.) are more likely to develop cancer than heart tissue whose cells don't divide at all. The age of cells varies.
Nerve cells of cerebral cortex, cells of eye lens and most muscle cells last a life time; once dead, they are not replaced. The cells of the skin are continuously lost. They are replaced every 2 weeks or so.
The life span of red blood cells is 120 days, platelets, 14 days and the average life span of white blood cells is 2 weeks. The cells lining the gut live only 5 days. The average life of other gut cells is 15 years and liver cells are replaced in 300-500 days.
Cancers happen when cells cease to obey the laws of cell division. This starts during cell division, when there is what is called mutation. So it is but natural that the chances of development of mutants are more in actively dividing cells and few in those that do not. The new gene is a foreign antigen.
The capacity to make an immunological response to a foreign antigen develops late in foetal life or even after birth; all potential antigens with which the cells are in contact during the period of immunological immaturity are recognized as self, while material with which the first contact is made after this period are recognized as ‘not-self' and will evoke an immunological response.
A cell born out of a mutation is recognized as ‘not-self' and destroyed by the same immunological mechanism which rejects a transplanted kidney or heart.
Dr. (Capt.) K.U. VINODAN
Thrissur, Kerala.
