What exactly is cancer?

“Cancer” is a term which still causes shock and fear when you hear it as a diagnosis. But what exactly is cancer?

Cancer is actually a group of diseases which have in common a loss of regulation of cell division, cell death, and cell migration. This loss of regulation usually arises because of damage to the DNA and so cancer, like genetically inherited diseases, can be though of as a disease of the DNA. In the case of cancer, the damage happens to genes which regulate either cell division (starting or stopping), DNA repair, cell maturation (differentiation) or cell death. Therefore, the cells with this damage can either divide endlessly or live a lot longer than their normal counterparts. This increased number of cells with uncontrolled growth is known as a tumour. They also like to migrate to nutrient rich organs. This is known as metastasis. Metastatic tumours behave like the original cancer cells, just in a new location. For example when osteosarcoma  (a type of bone cancer) cells migrate to the lung they still behave as osteosarcoma cells not as a type of lung cancer, and respond to the same type of treatment as the original osteosarcoma.

Cancers are grouped by the organ in which they arise (for example: skin cancer). They are further differentiated by the type of cell in which the uncontrolled growth is happening or the type of behaviour they exhibit. In the skin cancers these are squamous cell, basal cell (both which arise from the squamous epithelium in the dermis ) and melanoma (which arises from melanocytes). Each of these types of skin cancer behave quite differently and have a different prognosis  from each other. As more research is done, more differences are being found even within the traditional classification, which are reflected in differing responses to various treatments.

Because cancers are primarily diseases involving damage to particular genes involved in cell division you can encounter the same damage in different types of cancer. For example, you can have the same genetic damage in breast, ovarian and colon cancers involving the BRCA1 and BRCA2 genes. These types of cancers that have the same underlying genetic change can be said to be much more closely related than types of breast cancer with or without the BRCA1 & 2 gene involvement.

What controls normal cell division?

To understand what cancer really is, we need to first look at what makes cells enter cell division and what stops cell division if an error is found. The following chapters describe the process that cells undergo during replication and during cell differentiation. As you work through the next two chapters, think about what points of cell cycle control are important for normal function.

Section Summary

• Cancer occurs when damage happens to genes which regulate either cell division (starting or stopping), DNA repair, cell maturation (differentiation), or cell death. As a result, cells with this damage experience uncontrolled growth.
• Terminology of cancer is based first on the organ which the cancer arises and then sub-classifed based on the original cell which the cancerous DNA damage has occurred.
• Commonality of cancers are based on the similar gene which is damaged and not based on the organ from which it arose.

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