What Is Cancer?

I know a lot of onco-families are unfamiliar with the mechanics of cancer, we certainly were. I thought I would put together a short post explaining what cancer is.




I know a lot of onco-families are unfamiliar with the mechanics of cancer, we certainly were. I thought I would put together a short post explaining what cancer is. It does not cover the minutiae of cell division or growth, but rather the larger themes it helps to be familiar with. I will try to write another post specific to rhabdoids (MRT and AT/RT) soon. I hope this helps.


What is Cancer? Cancer is uncontrolled division and growth of abnormal cells in the body. It can come in the form of solid masses (tumors) or can occur in the blood forming tissues. Cancer can be caused by environmental factors, spontaneous mutations, or by a hereditary condition. All cancer, by definition, is genetic, meaning that it is caused by a change to the genes responsible for cell function. This makes cancer very difficult to treat, because each person’s cancer has its own unique series of mutations; even different cells within the same cancer may have different genetic mutations.


There are three types of genes that are very important when understanding how cancer works, proto-oncogenes, tumor suppressor genes,and DNA repair genes. When genetic changes occur in these genes they tend to contribute to the spread of cancer. They are often called “cancer drivers.” First are the proto-oncogenes. Proto-oncogenes code for proteins that regulate cell-growth and differentiation (cells growing into other cells). When a proto-oncogene has a mutation it called an oncogene. Oncogenes can cause uncontrolled cell growth or contribute to a malignancy. You can think of it as a light switch stuck in the “on” position. Next, we have tumor suppressor genes. Exactly what it sounds like. Tumor suppressor genes have a repressive effect on cell growth and promote apoptosis, or programmed cell death. This means cells which have certain mutations in these genes can no longer repress tumors, or keep cell growth in check.  So, if we stick with our light switch example, you can think of it as the knob broke off when it was switched on. Finally we have DNA repair genes. These genes are responsible for fixing damaged DNA. When there is a mutation in these genes they cannot repair genetic damage, for example, a lesion on a tumor suppressor gene. A normal DNA repair gene would attempt to repair the lesion or promote the death of the cell with the mutation, if there is a defect in the repair gene this does not happen. Essentially there is no way to repair the light switch or disconnect it. When cancer spreads it is called metastatic.The cells that make up the cancer will have similar genetic markers despite being in a different organ, or section of the body. If, for example, breast cancer spreads to a lung, it is still metastatic breast cancer, not lung cancer. Your child’s cancer could be due to a mutation in a proto-oncogene, tumor suppressor gene, and/or DNA repair gene, caused by a spontaneous mutation, an inherited predisposition, or an environmental factor. Most experts agree that most childhood cancer is caused by either a spontaneous mutation or an inherited condition, and is rarely environmental. More than likely it is a spontaneous mutation. Spontaneous mutations can occur in any cell, when they occur in germline cells, it is called a germline mutation. When a spontaneous mutation happens in any other cell it is called a somatic mutation, or an acquired mutation. The main difference is that germline mutations are in every cell and can be inherited by future offspring, while somatic mutations are not in every cell and are not inherited. Hereditary cancers, resulting from germline mutations, only account for 5%-10% of all cancers. According to a 2015 study from the St. Jude Children’s Research Hospital – Washington University Pediatric Cancer Genome Project, approximately 8.5% of pediatric patients may have a germline mutation. This mutation may have been passed down through a parent or a spontaneous mutation, meaning they would be the first person to have a hereditary cancer. Genetic testing can be used to identify a hereditary cancer, and help you decide who in your family should receive further testing. Some papers I have read discuss mosaic germline mutation. Mosaicism means that the mutation is not in all of the cells. There would be one set of cells which contain the mutation and another set which do not. There does not seem to be a consensus on what this means for cancer patients, or even if there is a consistent way to test for mosaicism. We will have to wait for more research.

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