Colon cancer. Rectal cancer. Colorectal cancer. Are these different names for the same type of cancer? Or is each a distinct type?

"Both colon cancer and rectal cancer share many similarities, including symptoms, certain risk factors and even some of the basic biology as to how these cancers develop. They're also screened for in a similar way. For these reasons, colon and rectal cancer are often grouped together as colorectal cancers," explains Dr. Monica Desai, medical oncologist at Houston Methodist. "However, there are differences between these two cancers, particularly when it comes to how they're treated."

Put another way, colon cancer and rectal cancer are both colorectal cancers, but colon cancer and rectal cancer, while similar, aren't exactly the same.

Dr. Desai is here to help break down some of the major similarities and differences between these two colorectal cancers.

How colon cancer and rectal cancer are similar

Colorectal cancers share similar symptoms, including changes in bowel habits, blood in stool, as well as many of the same risk factors.

But the similarities don't stop there.

Colon and rectal cancer begin in the same organ — the large intestine

Your large intestine is the final portion of your digestive tract. It's also where your colon and your rectum are located.

Your colon makes up the vast majority of your large intestine, and it's where water and the remainder of nutrients are absorbed and where stool is formed.

Your rectum is the final few inches of your large intestine. This is where waste that has passed through your colon is stored until being excreted during a bowel movement.

"Both colon and rectal cancer begin in the long muscular tubing that makes up the large intestine. Specifically, colon cancer begins in the colon and rectal cancer begins in the rectum," says Dr. Desai. "However, since the lower segment of the colon continues directly into the rectum, it takes special expertise to distinguish a cancer in the distal colon from rectal cancer."

Colon and rectal cancer start as polyps

Generally speaking, cancer begins when cells of the body grow uncontrollably.

In the case of colon and rectal cancers, the vast majority start as polyps — growths that develop in the interior wall of the colon or rectum.

"Both the colon and rectum are surrounded by a wall that's made up of many layers. Polyps can develop on the innermost layer of this wall, and they can either be benign or, over time, turn cancerous," explains Dr. Desai. "As the cancer grows, it moves into the layers of the colon or rectum. Within these layers, the cancer can then gain access to the circulatory system — which allows it to spread to distant parts of the body — or it can continue invading through these layers and spread to nearby tissue and organs."

Screening for colon and rectal cancer is the same

Possibly one of the most important similarities of these cancers are the screening methods used to find them. From stool tests to imaging procedures, both colon and rectal cancer are identified the same way.

"In particular, colonoscopy is the most trusted and effective way of catching colorectal cancers — whether in the colon or rectum," says Dr. Desai. "A colonoscopy can not only identify polyps growing in either segment of the large intestine, but theses polyps, if detected, can be removed using special tools right then and there."

And since most colorectal cancers begin as polyps, following the recommended screening guidelines is critical for both colon and rectal cancer.

"Early detection of colorectal cancer is so important. When these cancers are caught early, it can often mean less aggressive treatment, as well as a significantly better chance of survival," adds Dr. Desai. "A screening colonoscopy may sound uncomfortable, but it can save your life."

Depending on your family history, screening can begin as early as 10 years before the age at which a family member was diagnosed with colon or rectal cancer. For most, colorectal cancer screening begins at the age of 45 or 50, depending on your individual risks.

How colon cancer and rectal cancer differ

While the many similarities between colon and rectal cancer have resulted in these cancers being grouped together as colorectal cancers, the two individual cancers aren't completely identical.

The major difference between colon and rectal cancer is how they're treated, which can also vary depending on the stage of either type of cancer.

"Surgery is the cornerstone of treating both of these cancers, but the difference lies in whether — as well as when — chemotherapy and/or radiation may be needed as part of treatment," explains Dr. Desai.

Colon cancer is treated via surgery, which may or may not be followed by chemotherapy. When chemotherapy is used after surgery, it's called adjuvant chemotherapy.

"Radiation generally isn't part of treatment for colon cancer," adds Dr. Desai.

Rectal cancer treatment, on the other hand, often begins with either chemotherapy or radiation (or a combination of the two) before surgery. This is called neoadjuvant therapy. After surgery, more chemotherapy may be needed as well.

"Over the last several decades, rectal cancer outcomes have improved due to this up-front decision-making about whether neoadjuvant therapy might benefit treatment, as well as whether this neoadjuvant therapy should be chemotherapy, radiation or a combination of the two," says Dr. Desai.

But even with these treatment differences, Dr. Desai reminds us of one primary reason colon and rectal cancers are grouped together: The importance of screening colonoscopy for catching both types of cancer.

"The most important thing for people to understand is how important colorectal cancer screening is for detecting both colon and rectal cancer early — when each is easiest to treat," emphasizes Dr. Desai.