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What is colorectal cancer?

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The term cancer encompasses a very large group of illnesses that are all characterised by abnormal cell growth; cancer cells divide and grow in an uncontrolled manner and in any part of the body. Most colorectal cancers (called adenocarcinomas) derive from disorderly growth of cells covering the large intestine.

Anatomy of the colon and rectum

Anatomically speaking, the colon is comprised of different sections, called the caecum, ascending colon, transverse colon, descending colon, sigmoid colon and rectum, as we move from the most proximal (i.e., the portion nearest the small intestine) to the most distal sections (closest to the anus).

The colon is attached to the rear of the abdomen via a structure called the mesentery which provides mobility. The rectum, by contrast, is stationary as it is located inside the pelvic cavity and therefore delimited at the back by the sacrum and at the front by the urinary bladder, prostate and the seminal vesicles in men or the uterus and vagina in women.

At a microscopic level, we can distinguish different layers in the walls of the colon and rectum. Moving from the inside to the outside of the intestine we find the mucous, submucous, muscular and serous layers. Cellular invasion of these various layers will give rise to different tumour stages, which consequently has an impact on the patient’s prognosis.

The main function of the colon is to absorb water and minerals. This process increases stool consistency, while the rectum is responsible for faecal continence. Internal and external anal sphincter function is essential for continence. The internal sphincter acts involuntarily, while the external sphincter relaxes according to the individual’s voluntary control, thus facilitating defaecation.

Types of colorectal cancer

Most of the points addressed in this pathology monograph are common to both cancers of the colon and rectum, which is why they are typically called colorectal cancers. However, the progression pattern, and consequently the treatment guidelines and prognosis, can vary according to whether the cancer is located in the colon or the rectum due to their anatomical differences.

Colon cancer primarily spreads over a distance, giving rise to metastasis (propagation from the cancer focus to an organ other than where it initially developed), particularly to the liver. That is why treatment usually involves surgical removal and the administration of complementary chemotherapy.

Rectal cancer, on the other hand, presents a greater likelihood of locoregional progression due to the proximity of other structures found in the pelvic cavity and consequently treatment generally includes radiotherapy and chemotherapy, before or after surgical removal. If distant metastases develop, then they tend to occur in the liver (tumours located in the upper third of the rectum) or the lungs (tumours originally situated in the middle or lower thirds of the rectum).

Overall, the prognosis for colon cancer is more favourable than for rectal cancer, but it essentially depends on the tumour stage at the time of diagnosis.

How many people are affected by colon and rectal cancer?

Considering both sexes together, colorectal cancer is the most frequently diagnosed of all tumours. Taking each sex separately, colorectal cancer is the third most common type of cancer in men, after prostate and lung cancers, and the second most in women, after breast cancer. Over 28,000 new cases are diagnosed in Spain every year.

Despite significant advances in its treatment, colorectal cancer is still the second highest cause of all cancer deaths. In fact, each year more than 15,000 people in Spain die due to this disease.

Colorectal cancer is generally first diagnosed in people aged between 60 and 70 years. By contrast, if there is a family history of this type of neoplasm, and especially when the tumour develops in the context of a hereditary disease, then the onset is earlier, usually before the age of 50. It is a disease that affects both men and women, although the prevalence is slightly higher in men.