What Is Cancer?
The ancient disease that is cancer has become a word intertwined with fear and dread. It is often described as the defining plague of our generation and one affecting tens of millions, killing approximately 9.5 million people every year. An incurable spreading ulcer, crab-like in shape, was assigned the Latin name “Cancer” by the Ancient Romans, although records of the disease have been discovered to trace to significantly earlier periods of time.
Fundamentally, cancer is a condition where cells in a specific part of the body grow and reproduce uncontrollably. Cancerous cells tend to invade surrounding healthy tissue and organs, damaging and destroying them. The process in which these cancerous cells spread from a specific area to an exceedingly large is known as metastasis and is one of the principal reasons why cancer is so hard to treat and may be so lethal.
Although it is often referred to as if it is only one disease, there are in fact more than 200 different types of cancer, with the 5 major types including Carcinoma, Sarcoma, Melanoma, Lymphoma and Leukaemia.
Named after Epidemiologist Richard Peto, who made pioneering advancements in discovering correlations of cancer with time and other crucial discoveries, Peto’s Paradox remains unanswered till today.
Peto’s Paradox revolves around the discovery (made by Peto) that although humans lived 30 times longer and had 1000 times more cells than mice, the two species did not suffer incredibly different probabilities of developing cancer. In fact, large animals such as blue whales appear to be immune to cancer.
This is paradoxical because probability-wise, an organism with more cells and a longer life span should be more prone to cancer. More cells means more genetic information and mutations; and a longer lifespan implies that there is more time for these mutations to accumulate, producing more cancerous cells.
Basics of Carcinogenesis
To understand the paradox in greater detail, one must understand how cancers are formed; or Carcinogenesis/ Essentially, Cancer is caused by the accumulation of damage to genes. Although during the life of an organism, healthy cells will constantly divide and replace themselves in a controlled fashion, there are always DNA copying errors being made during protein synthesis. According to research done by the John Hopkins Kimmel Cancer centre, most cancer mutations result from these DNA copying errors that accumulate during one’s lifetime.
Genes – genetic instructions – control the way a cell behaves, including what it produces, when it will divide and when it will die. However, when division occurs, mutations may sometimes occur. Mutations are when a change happens in the genes when being copied? changes such as damage, loss or copying the gene twice. Mutations may happen by chance and although most will be corrected or inconsequential to the cell’s function, some mutations (especially those in the Proto-Oncogenes) will lead to the uncontrollable reproduction of cells. Mutations and accumulated damage are part of the first stage: Initiation.
Mutations have to accumulate until there has been about half a dozen different mutations before normal cells turn into cancer cells if Apoptosis (“cell suicide” for when the cell is perceived to be a threat to health”) doesn’t occur. This is known as the Transformation stage. Metastasis or the Progression Stage then occurs, establishing multiple tumour sites.
So how are Blue Whales immune to Cancer?
According to the fundamentals of carcinogenesis above, it is only logical that an organism with more cells will experience more mutations and more accumulated genetic damage. Therefore, large animals with long life spans such as Blue Whales and Elephants should be more liable to cancer. There are 2 main theories for why larger animals have a lot less cancer than they should: Evolution & Hyper-tumours.
One theory that is widely accepted is that as animals started to increase in size 65000 years ago, animals had to evolve to survive the risks of being so big; with a crucial risk being the high probabilities of getting cancer. Therefore, the process of evolution has caused those (species and individuals) with weaker cancer defences to die out.
The principal evidence that backs up this theory is the discovery of higher frequencies of Tumour Suppressor Genes in elephants. Tumour Suppressor Genes are the antagonist genes to Proto-Oncogenes (the genes that transforms healthy cells to cancerous cells after mutation). They act against the Proto-Oncogenes by attempting to prevent mutations from happening to the Proto-Oncogenes and also to order cells to go through Apoptosis if its damage is beyond repair.
Research and investigations have shown that large animals have an increased number of these Tumour Suppressor Genes, meaning that: Elephantine cells require more mutations to develop a tumour. They are not immune, but more resilient to cancer.
Another widely accepted theory is the theory that larger animals may be filled with tumours but may have no health problems due to Hyper-Tumours. Named after hyper-parasites(the parasites of parasites), hyper-tumours are the tumours of tumours. As tumours grow, their limiting factor is the amount of nutrients from the body it can get as it requires a lot of nutrients and energy to rapidly reproduce.
Hyper-tumours are when a single or a group of cancerous cells break from the main tumour to form their own tumour. They disconnect nutrient supply pathways, taking over, causing the main and previous tumour to run out of energy to spread and carry on its rapid division, eventually leading to its destruction. This allows a numerous number of tumours to develop, with none doing any harm as they are replaced by another tumour before they become so large that they affect the health of an animal.
Cancer In Other Animals
Cancer is a disease that is present in nearly all animals and also in many plants (although the cancer cannot metastasize as plant cells cannot move). However, cancer is different for many organisms.
1. Contagious Cancer
Clams, cockles, Tasmanian devils and dogs can all “catch” cancer. There are specific types of cancer that cause ‘transmissible tumours that may pass on from one individual to another.
2. Cancer Resistant Animals
Bow-head whales can live up to 200 years and are immune to cancer.
Elephants have 20 copies of a tumour suppressor gene that humans only have 1 of.
However, Naked Mole Rats, although small, are also immune to cancer.
Hope for Humans?
Advancements in genetic engineering and our knowledge of this ancient yet perplexing disease has allowed us to conduct pioneering research to analyse the disease further. And although we are still analysing other animals in order to learn; we should be hopeful to see a more effective treatment for the disease in the foreseeable future.