Not An Old Person's Disease

Judy did a little research about skin cancer on the Internet before her doctor's appointment the next morning.  She learned that most cases occurred in people who were significantly older than she was.  It didn't make sense that it would happen to her—she was only 20 years old!

The articles talked about how UV light from the sun causes mutations in your DNA.  Accumulation of DNA mutations over many years can cause certain cell cycle genes called "proto-oncogenes" to become super-active.  Judy actually felt thankful for the college biology course she had been forced to take.  She knew that DNA was the hereditary material that acted as a "blueprint" for everything our cells make and that a gene is a piece of DNA that contains the instructions for making a single protein.  However, she would have to ask the doctor about these proto-oncogenes.

In the examining room, Dr. O'Brien was silent as he looked at the mole on her leg.  Finally, he said kindly, "I want to do a biopsy.  All that means is we'll remove your mole and look at the cells under a microscope and see if they look abnormal."

Judy could feel the tears welling up in her eyes.  "You mean you can tell if I have a tumor by just looking at some cells?"

"Whoa, slow down a minute," Dr. O'Brien replied calmly.  "It's very possible that your cells will look completely normal.  And to clarify something, a tumor is not necessarily the same thing as cancer."  She looked confused, so he continued.  "A tumor means that cells have divided and piled up on one another in a single mass.  But not all tumors are automatically cancerous and life threatening.  A benign tumor is a mass of normal-looking cells.  These tumors are not considered cancer and they're usually relatively easy to treat—we just remove them.  On the other hand, a malignant tumor is a mass of abnormal cells whose growth cannot be controlled by the regular mechanisms.  In addition, malignant tumors often spread to other parts of the body instead of just staying in one spot.  We call this process metastasis.  Malignant tumors are cancerous and, therefore, a very serious condition.  To treat them, we have to remove the cancerous cells that we find and then do chemotherapy treatments to be sure to kill all the cancer cells that we may have missed surgically."

"So, if I have cancer, is it from these proto-oncogenes that I read about on the Internet?"

The doctor smiled and seemed pleased that Judy had been reading about this on her own.  "Let's back up for a minute.  You see, we have tens of thousands of genes in our cells, but it's not like mutations in just any of them will lead to cancer.  The genes that get mutated and can cause cancer are of a specific type called cell cycle genes.  Everyone has a set of cell cycle genes in each of their cells that code for cell cycle proteins.  Cell cycle proteins control if and when cells divide.  Sometimes we need to make more cells in our bodies, and some of these cell cycle proteins allow that normal process of cell division to occur.  At other times we don't want the cells to divide, so different cell cycle proteins inhibit cell division then.  In normal, healthy cells, the formation of the cell cycle proteins is tightly controlled so the activating proteins are only made when we really need more cells and the inhibitory proteins are only made when we don't need more cells.  However, mutations (or alterations) in these genes can eliminate this tight regulation and lead to uncontrolled cell division.  This is what happens in many types of cancer:  a normal cellular process, cell division, is no longer properly controlled."

Judy thought for a second.  "Okay, but you still didn't say what these proto-oncogenes are."

"Oh yes, sorry.  The activating class of these cell cycle genes consists of the proto-oncogenes.  The normal job of these genes is to code for proteins that promote cell division.  Certain mutations in proto-oncogenes result in proteins that are active all the time, causing cells to divide continuously.  But let's not get ahead of ourselves—we won't know if your mole is even cancerous until we do the biopsy."

When Judy didn't say anything in response right away, Dr. O'Brien continued, "I know this is all a bit confusing, but it's good that you're asking these questions.  We'll make sure that you understand this a little better before you leave today."

Just then a nurse knocked and entered the room.  He needed Dr. O'Brien for a minute.  At least Judy would have a minute to gather her thoughts.

Questions

1. Considering the differences between a benign tumor and a malignant tumor, why might a benign tumor be easier to treat?
2. Judy learned that every single person has these cell cycle genes so cells in our body can divide when necessary.  What are some normal circumstances where our bodies might need to make more cells?
3. Every person has these cell cycle proto-oncogenes, but not every person has cancer.  Why might this be the case?

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