Malignant ascites accounts for approximately 7-10% of all cases of ascites. A number of mechanisms exist whereby cancer can cause ascites, and its development is not always synonymous with a diagnosis of peritoneal carcinomatosis. The two main causes observed in the Beatson West of Scotland Cancer Centre are:
Patients often seek medical attention because of symptoms such as:
Weight loss will often be recounted prior to the development of ascites.
The presence of bulging flanks, a distended / firm abdomen, or an everted umbilicus should lead to percussion for dullness and testing for shifting dullness.
Avoid serum CA125 testing as it is often falsely elevated in the presence of ascites. In fact, virtually all patients, including men, with ascites or pleural fluid of any cause have elevated serum level of CA125. In ovarian cancer, CA125 should not be used to monitor response for at least 28 days following a paracentesis.
Positive ascitic fluid cytology is needed to establish the diagnosis of malignancy-related ascites, if this is in doubt e.g. a patient with a history of cirrhosis. The overall sensitivity of cytology for the detection of malignancy-related ascites is 58–75%.
Send ascitic fluid for investigation to help confirm diagnosis and exclude infection. These include:
The sample volume sent to pathology should exceed 200ml if possible, as sensitivity for a diagnosis of malignant ascites increases with larger sample volumes.
Bacterial culture is particularly important in those with fever or abdominal pain, although it should be noted that peritoneal carcinomatosis can sometimes mimic spontaneous bacterial peritonitis. Initially give antibiotics when an elevated fluid neutrophil count is detected, but discontinue when it becomes clear (by positive cytology and absence of growth on bacterial culture) that ascites is related to malignancy and not infection. Ascitic fluid will be macroscopically bloody in 20% of cases.
Ascites in women with a new diagnosis of epithelial ovarian cancer is not necessarily associated with a severely limited prognosis; such patients may live for years once appropriate anti-cancer treatment is established. When a patient develops ascites in the setting of a non-ovarian cancer, the prognosis is usually poor and often less than three months.
In women with a new diagnosis of epithelial ovarian cancer, the initial treatment of choice is surgical debulking with chemotherapy. In the presence of large volume ascites, or if surgical debulking is not feasible then primary chemotherapy can be given with delayed primary surgery after 3 cycles of chemotherapy.
In patients with malignant ascites secondary to other solid tumours, prognosis is generally poor and the role of surgery is not established. Palliative systemic therapy is sometimes appropriate, with the treatment regimen tailored towards the primary site of cancer.
Abdominal paracentesis with appropriate ascitic fluid analysis is the most efficient way to diagnose cause, and determine if ascitic fluid is infected. Repeated abdominal paracentesis is sometimes needed for women with ovarian cancer, while chemotherapy treatment is established, with the frequency of drainage again guided by the patient's symptoms. For patients where chemotherapy is unlikely to be effective and who require repeated drainage, an indwelling catheter should be considered. When undertaking paracentesis:
Patients often have a poor appetite and thus a diet to maximise caloric intake should be considered. Patient with co-existing bowel obstruction may require parenteral nutrition.
Consider if there is peripheral oedema or refractory ascites. They are more likely to be effective if portal hypertension is contributing to the pathophysiology of the ascites. Diuretics may cause hypotension and intravascular depletion so response must be monitored on an individual basis. Spironolactone oral 100mg daily is the suggested initial dose, with titration upwards as necessary. U&Es must be closely monitored as necessary. Furosemide can be considered as an alternative if hyperkalaemia develops.
Guideline reviewed: August 2023
Page last updated: December 2023