Nausea and vomiting are common, distressing symptoms experienced by individuals with cancer. The causes stem from a complex interplay of factors, broadly separated into those driven by the physical presence of a tumor and those resulting from medical interventions. Understanding the underlying mechanism is important for effective management, as these symptoms can severely impact a person’s quality of life and nutrition.
Cancers Causing Vomiting Through Physical Obstruction
Tumor growth within or adjacent to the digestive tract can physically impede the normal passage of food and waste, causing malignant bowel obstruction. This mechanical blockage causes contents to back up, leading to distension of the stomach and intestines, which triggers the vomiting reflex. The location of the obstruction dictates the specific symptoms and tumor type involved.
Tumors in the stomach near the pylorus can cause gastric outlet obstruction. The mass narrows the exit, preventing food from emptying into the duodenum. This results in vomiting of undigested food, often providing temporary relief.
Pancreatic cancer, especially in the head of the pancreas, frequently causes vomiting through external compression. The tumor mass presses against the duodenum, the first part of the small intestine. This pressure creates a bottleneck, leading to a buildup of material.
Advanced colorectal cancer can cause a lower bowel obstruction when the tumor mass blocks the colon’s lumen. The intestine proximal to the blockage distends, generating intense pressure and cramping. Vomiting occurs later than in upper GI causes and may contain material from deeper within the digestive tract.
Cancers Causing Vomiting Through Neurological Pressure
Vomiting can originate from the central nervous system due to tumors located in the brain. The rigid nature of the skull means any growing mass, primary or metastatic, increases intracranial pressure (ICP). This pressure elevation triggers the vomiting center and the adjacent chemoreceptor trigger zone (CTZ) in the brainstem.
Metastatic tumors that have spread to the brain are a common cause of this neurological vomiting. Primary sites like the lung, breast, and melanoma frequently spread to the brain tissue. As the tumor and surrounding edema occupy space, the brainstem is compressed, stimulating the area responsible for initiating emesis.
This neurological vomiting has specific characteristics distinguishing it from gastrointestinal causes. It is often worse upon waking, when ICP is naturally higher after lying down. The vomiting may also be projectile, expelled with force and without the preceding nausea common in stomach-related emesis.
Vomiting Induced By Cancer Treatments
Cancer treatments are the most common source of emetic symptoms for many patients. Chemotherapy-induced nausea and vomiting (CINV) results from potent drugs targeting rapidly dividing cells, including those lining the gastrointestinal tract. This damage causes the release of serotonin from gut cells, which signals the vomiting center in the brain via the vagus nerve and the CTZ.
Chemotherapy agents are classified by their emetogenicity, or risk of causing vomiting, ranging from highly emetogenic agents (like cisplatin) to low-risk agents. This classification determines the prophylactic anti-emetic regimen administered before treatment. CINV timing is categorized into three distinct phases:
- Acute vomiting occurs within the first 24 hours following infusion, typically peaking within five to six hours.
- Delayed vomiting begins more than 24 hours after treatment, often lasting several days, and is associated with agents such as cyclophosphamide.
- Anticipatory vomiting is a conditioned psychological response occurring before a new cycle of chemotherapy, often triggered by clinic sights or smells, following poorly controlled previous symptoms.
Radiation therapy can also induce vomiting (RINV), though it is generally less severe than CINV. The risk relates directly to the treatment site and the volume of tissue irradiated. Radiation directed at the abdomen or pelvis carries the highest risk because it involves a large portion of the gastrointestinal tract. Treatment to the brain also poses a risk due to potential stimulation of central vomiting pathways.
Strategies for Managing Nausea and Vomiting
Effective management of cancer-related emesis relies on combining drug regimens with supportive care techniques. Pharmacological intervention focuses on pre-emptively blocking the chemical signals that trigger the vomiting reflex. For high-risk treatments, a combination of medications is used, including serotonin (5-HT3) receptor antagonists, neurokinin-1 (NK-1) receptor antagonists, and corticosteroids like dexamethasone.
These anti-emetic medications target different neuroreceptors involved in the emetic pathway to control acute and delayed symptoms. Non-pharmacological strategies complement drug therapy by addressing behavioral and environmental factors. Simple dietary adjustments, such as eating small, frequent meals, avoiding strong odors, and consuming bland foods, can help minimize gastric irritation.
Behavioral interventions, including relaxation techniques, guided imagery, and acupuncture, may also be incorporated to help manage anticipatory symptoms. Patients must seek immediate medical attention if vomiting becomes relentless or is accompanied by other severe symptoms. Signs like severe dehydration, inability to keep down oral anti-emetic medication, or vomiting blood necessitate urgent clinical evaluation.