NORMAL GROWTH AND DEVELOPMENT AND NEOPLASIA (‘NEW GROWTH’)

From the first division of the fertilised egg cell until the death of the adult human decades later, a single copy of the original diploid genome needs to be replicated countless times to allow for growth of the embryo, fetus, neonate, child, adolescent and adult (consisting of about a hundred trillion offspring from that original fertilised egg cell), and also for the maintenance of cell numbers to replenish those lost through normal use and wear and tear (for instance we replace 250 thousand million red cells every single day, which is about three million each second, and that's just the red cells!). It is truly astonishing that this is generally accomplished with the exquisite precision that we tend to take for granted, especially when we understand that theoretic ally it just takes a single mistake in the copying of a single base, if that base is critically located in a growth-controlling gene, in a single cell of our complement of a few trillion, to set in motion a chain of events that may result in the growth of a malignant tumour that may kill us. Evolution has provided us with an elaborate set of fail-safe devices that usually obviate this catastrophe, but the sad reality is that some - times even these break down and the result is a single cell freed from the growth constraints that are normally imposed on it as a component of the complex social cellular structure that is a human being. From that moment, that cell and its rapidly expanding progeny (the malignant clone, or cancer) go it alone, as it were, and follow an evolutionary pathway dictated entirely by the survival of the clone, oblivious or even antagonistic to the welfare of the host that spawned them initially. It behaves much like a foreign organism in com - petition with its host, but unlike other foreign organisms this new growth, or neoplasm, is so much like the host immunologically that the immune system fails to recognise it as any kind of a threat, and does little or nothing to curb its growth.