Cancer in cats. Part one.
Please note that you are reading the old version of this article. You can find the updated article here.
According to Animal Cancer Foundation, 1 in 5 cats will develop cancer in their lifetime. Cancer in cats is actually less common than cancer in dogs, but once it is diagnosed, it tends to move faster. Since cats are the closest mammals to humans (outside of primates, of course) it is no wonder cats share many of the same cancers with us. Knowledge is power, and how much do we really know about signs of this deadly disease in feline?
Our blog post is split in two parts. In Part 1, we will cover some of the basics below:
1) Cancer vs. tumor?
2) How does cancer develop?
3) What is the cause of cancer in cats?
Part 2 will go more into details on treatment and what to do to protect our pets from cancer.
Our role as pet parents is to be armed with information. Let’s dig deeper to understand a bit more about feline cancer.
Cancer vs. tumor?
Is there a difference between tumor and cancer? The answer is yes.
Abnormal cell growth results in formation of the tumor (also known as neoplasm). Tumors can either be malignant or benign. Malignant tumors are invasive and have a potential of spreading to other parts of the organism. On the contrary, benign tumors are less invasive and do not spread through the body (Figure 1).
Cancer is a malignant type of tumor. Therefore, cancer is defined as a disease marked by abnormal and uncontrolled cell division that potentially invades and spreads to other parts of the organism.
Figure 1: Benign tumor vs. malignant tumor/cancer
How does cancer develop?
The fundamental cause of tumor formation in any organism lies in the accumulation of DNA mutations and epigenetic alterations in a cell. This further leads to abnormal cell division and eventually – tumor formation. Therefore, for a healthy cell to transform into a cancerous cell, the genes that control its division and differentiation must be altered.
Genes that are involved in the formation of cancer are divided into two categories: oncogenes and tumor suppressor genes. Oncogenes promote cell growth and division. Tumor suppressor genes inhibit cell reproduction and its survival. To put it as simple as possible: malignant transformation can be a result of over-expression of oncogenes and/or under-expression of tumor suppressor genes (Take a look at Figure 2). For a complete cell transformation, however, alterations in multiple genes are typically required.
These changes can occur by different mechanisms. Most common mechanism of gene alterations is through mutations. Mutations represent permanent changes in the nucleotide sequence of the genome. DNA mutations are very diverse and they can be caused by many factors on different levels of DNA organization. There are a lot of classifications of mutations based on various criteriums out there, but we will mention only the one that divides them into two categories: large-scale and small-scale mutations.
Large-scale mutationsinclude mutations on the chromosome level. They involve loss or gain of a portion of a chromosome, as well as translocations of its regions to a different location on the same or different chromosome.
Small-scale mutations include point mutations and INDEL mutations (insertions and deletions). These mutations can either occur in the coding sequence of the gene and alter the function and/or stability of its protein, or they can occur in the promotor region and alter the level of expression of the given gene.
Figure 2: Series of mutations leading to cancer development
Mutations occur fairly frequently in all cells. However, cells possess error-correcting machineries that recognize the mutations and "fix" them. If the error is not fixable, then the cell is marked for apoptosis – controlled and programmed cell death. This way the accumulation of mutations is prevented.
If initial errors compound into more severe errors, a cell is escaping more and more controls that limit her growth and division. This chain reaction can eventually lead to a cell transformation. Once the cell is transformed, unless killed by the organism shortly after, it will divide and form a neoplasm.
What causes cancer in cats?
The causes of cancer in cats are generally unknown. Feline leukemia virus (FeLV) is suspected to be a prime contributor, alongside environmental toxins, second hand smoking and excessive grooming. Hormonal status and some breeds have been linked to the higher risk of developing certain forms of feline cancer too.
FeLV is one of the most common feline viruses, alongside feline immunodeficiency virus (FIV). "FeLV adversely affects a cat's body in many ways. It is the most common cause of cancer in cats, may cause various blood disorders, and may lead to a state of immune deficiency that hinders a cat's ability to protect itself against other infections." – Cornell Feline Health Center - "Fortunately, the prevalence of FeLV in cats has decreased significantly in the past 25 years since the development of an effective vaccine and accurate testing procedures."
It is important to note that any factors that are linked to cancer do not necessarily cause cancer. They simply increase the risk of developing cancer. And usually, multiple different factors play a role in cancer development. This is why the answer to the question "what causes cancer" is nearly impossible to properly answer.
As you can see, cancer is a complex disease that sneaks up on a patient in a slow and complex pathway. Next week, we will cover a bit more about how to prevent cancer in your pets, and what to do once cancer has been spotted.