The digestive system includes the gastrointestinal (GI) tract, liver, and pancreas. Cancer affects this system in varied ways, whether originating locally, spreading from other locations, or resulting from medical interventions. The physical and chemical processes of digestion can be compromised at every stage. Understanding this impact requires looking beyond the immediate physical presence of a tumor to include systemic functional changes and the side effects of therapy, which affect overall health and nutritional status.
Structural Damage and Obstruction
A tumor mass directly compromises the structure and passage function of the GI tract. Growth within hollow digestive organs can narrow the passageway, leading to an obstruction. In the esophagus, a growing mass causes dysphagia, or difficulty swallowing, initially for solids and eventually for liquids.
Colorectal masses can create a malignant bowel obstruction, impeding the passage of stool and gas. This blockage occurs when the tumor fills the lumen or when surrounding scar tissue and inflammation tighten the bowel wall. Obstruction consequences include painful abdominal distension, nausea, and vomiting because contents cannot move past the tumor.
Tumors damage the digestive lining, often resulting in gastrointestinal bleeding. Cancer tissue forms fragile, abnormal blood vessels (pathologic angiogenesis) that are prone to rupture. Additionally, a tumor can outgrow its blood supply, causing central necrosis and ulceration that erodes into surrounding blood vessels. This bleeding may be visible, such as blood in the stool, or occult, meaning it is hidden and only discovered through laboratory tests, often leading to anemia.
Structural breakdown can result in perforation or fistula formation. Perforation occurs when a tumor completely penetrates the digestive organ wall, often due to tissue necrosis or extreme pressure near an obstruction. A fistula is an abnormal channel that forms between two organs or between an organ and the skin. This happens when a tumor erodes through the wall of one digestive structure into an adjacent one, such as connecting the stomach and the colon.
Systemic Functional Disruptions
Cancer initiates systemic changes that impair the body’s ability to chemically process and absorb nutrients. A primary example is malabsorption, often seen in pancreatic cancer, which causes Pancreatic Exocrine Insufficiency (PEI). When a tumor obstructs the pancreatic duct, it prevents digestive enzymes necessary to break down fats, proteins, and carbohydrates from reaching the small intestine.
Without these enzymes, especially lipase for fat digestion, food passes through undigested. This leads to weight loss, malnutrition, and fatty, foul-smelling stools known as steatorrhea. Another functional disruption is jaundice, which occurs when a tumor, often in the head of the pancreas, compresses the common bile duct. This mechanical obstruction blocks the flow of bile, which contains the yellowish waste product bilirubin, from reaching the small intestine.
The buildup of bilirubin in the bloodstream causes the characteristic yellowing of the skin and eyes, dark urine, and light-colored stools. Jaundice signals a blockage and impairs the body’s ability to absorb fat-soluble vitamins, which rely on bile for uptake. The most profound systemic functional change is cancer-related cachexia, a metabolic wasting syndrome distinct from simple starvation.
Cachexia is driven by systemic inflammation and pro-cachectic factors released by the tumor, which alter the body’s metabolism. This dysregulated state causes the involuntary loss of skeletal muscle and fat tissue. It is often accompanied by increased resting energy expenditure, meaning the body burns more calories at rest. This catabolic process resists conventional nutritional support and causes weakness.
Cancer can alter the digestive system’s motility, which are the coordinated muscle contractions that propel food through the tract. This dysfunction is not purely mechanical but can be caused by the tumor affecting nerves or through hormonal signaling changes. Furthermore, pain management, often involving opioid medications, frequently causes severely slowed motility, resulting in chronic constipation.
Digestive System Side Effects of Treatment
Medical interventions often inflict damage on the healthy, rapidly dividing cells of the digestive tract. Chemotherapy commonly causes chemotherapy-induced mucositis, which is the inflammation and breakdown of the mucosal lining throughout the GI tract. This damage to the intestinal barrier leads to side effects such as nausea, vomiting, and diarrhea.
Diarrhea results from impaired absorption and increased fluid secretion caused by damaged cells. Nausea and vomiting are triggered by the release of inflammatory mediators and the direct stimulation of the brain’s vomiting center. Radiation therapy, particularly to the abdomen or pelvis, can cause radiation enteritis, which is inflammation of the intestines within the radiation field. Acute enteritis occurs during or shortly after treatment due to direct cell death.
Chronic radiation enteritis can develop months or years later. The radiation causes fibrosis, scarring in the bowel wall, and small vessel damage, which can lead to strictures, obstruction, and chronic pain. Surgical interventions, especially those involving the stomach or esophagus, dramatically change digestive function. Operations like a gastrectomy, which removes part or all of the stomach, eliminate the stomach’s ability to store food and regulate its release into the small intestine.
This loss of reservoir function leads to dumping syndrome, where food, particularly sugary contents, is “dumped” too quickly into the small intestine. The rapid influx of concentrated food draws excessive fluid into the intestine, causing cramping, diarrhea, and a sudden drop in blood pressure. Rapid sugar absorption can later cause a reactive hypoglycemia. The removal of a section of the intestine or colon often necessitates an ostomy, a surgically created opening called a stoma on the abdomen to reroute waste.
A colostomy or ileostomy fundamentally alters waste elimination by bypassing the rectum and resulting in stool collection in an external pouch. For an ileostomy, where a significant portion of the large intestine’s water-absorbing function is lost, the output is more liquid. This requires careful management to prevent dehydration and electrolyte imbalances. These surgical changes require adjustments in diet and lifestyle to manage the altered digestive output.