Prostate cancer itself does not typically cause diarrhea. The prostate gland is located in the pelvis, in front of the rectum, and early-stage cancer usually does not affect bowel function directly. However, men undergoing treatment frequently experience bowel changes, including diarrhea. This occurs because the treatments designed to eliminate cancer cells often affect healthy, rapidly dividing cells in the digestive system. Understanding the true source of diarrhea helps in managing the symptom effectively.
Diarrhea as a Side Effect of Treatment
Most diarrhea cases in men with a prostate cancer diagnosis result from medical interventions aimed at eliminating the disease. These treatments target cell growth and division, a process that affects both malignant cells and healthy, rapidly regenerating cells. The intestinal lining is highly sensitive to these systemic and localized therapies.
Diarrhea is a frequent side effect of pelvic radiation therapy due to the prostate’s close proximity to the rectum. Radiation beams can unintentionally irritate or damage the rectal lining, causing inflammation known as radiation proctitis. This leads to increased stool frequency, loose bowel movements, and an urgent need to defecate. Approximately 60% of patients experience temporary mild diarrhea during treatment, and symptoms may persist for months or years after therapy ends.
Chemotherapy agents target rapidly dividing cells throughout the body, including the epithelial cells lining the gastrointestinal tract. When these cells are damaged, the intestine’s ability to absorb water and nutrients is compromised. Unabsorbed water remaining in the bowels results in diarrhea, which can lead to fluid and electrolyte depletion. Diarrhea may begin shortly after a chemotherapy session and typically lasts for one to two weeks, depending on the specific drug regimen used.
Hormone therapy, or Androgen Deprivation Therapy (ADT), can also cause changes in bowel habits, though these are generally less severe than those caused by radiation or chemotherapy. Newer hormonal agents (e.g., abiraterone, apalutamide, and enzalutamide) have been linked to a low to moderate risk of diarrhea. This is thought to involve alterations in the gut microbiome and, sometimes, bile salt malabsorption, disrupting normal digestive processes.
Cancer Progression and Bowel Changes
While treatment is the most common cause, bowel changes can occasionally be linked directly to the progression of prostate cancer. This is rare, typically occurring only in cases of advanced or metastatic disease. A prostate tumor is positioned to potentially impact the rectum if it grows significantly beyond the gland’s capsule.
A large, localized tumor can physically press on the rectum, leading to a feeling of incomplete emptying or changes in stool caliber, which may include diarrhea or constipation. In rare instances, cancer may spread directly to the rectum or nearby lymph nodes, causing inflammation or physical obstruction in the bowel wall. This direct involvement can disrupt the normal movement of waste through the colon. Metastasis to distant sites can also indirectly affect bowel function. If cancer spreads to the bones of the pelvis or spine, the resulting tumor mass can put pressure on the nerves controlling the lower bowel muscles. Extremely rare advanced cancers may release substances that impact gut function and motility, leading to bowel issues.
Managing Bowel Changes During Treatment
Managing diarrhea is important for comfort and preventing complications like dehydration and malnutrition. Dietary modifications are a primary intervention for mitigating loose stools. A temporary shift to a low-residue diet, consisting of foods like bananas, white rice, applesauce, and white toast, helps reduce the amount of undigested material passing through the colon.
It is helpful to avoid foods that irritate the digestive tract or increase intestinal motility. These include:
- High-fat, fried, or spicy foods.
- Products containing dairy.
- Caffeine.
- Alcohol.
Eating smaller, more frequent meals, rather than three large ones, can also make digestion easier. Patients should separate liquid intake from solid food consumption by about 30 minutes to improve nutrient absorption.
Replacing lost fluids and electrolytes is important to prevent dehydration. Drinking clear liquids, such as water, broth, and sports drinks, helps replenish the body’s stores of sodium and potassium. Over-the-counter anti-diarrheal medications, most commonly loperamide, are often recommended as a first-line treatment for managing symptoms.
Any use of medication should be discussed with a healthcare provider, especially during chemotherapy, as some drugs can mask serious underlying issues. Contact a doctor immediately if diarrhea is severe, lasts longer than 48 hours, or is accompanied by fever, blood in the stool, or signs of severe dehydration (e.g., dizziness or dark urine). These symptoms may indicate a need for prescription medication, intravenous fluids, or a change in the treatment plan.