Metastases to Abdominal-Pelvic Organs

Introduction

Metastasis is a complex process in which tumor cells leave the original site of disease, called the primary tumor, to spread to other parts of the body. Cancer cells can break away from a primary tumor, enter the blood vessels, circulate through the bloodstream, and be deposited in other organs far from the primary tumor. When tumor cells metastasize to distant organs, the new tumor is called a secondary or metastatic tumor.

Epidemiology

Most tumors can metastasize. The most common sites of metastasis from solid tumors are the lungs, liver, and bones. However, the frequency, location, and patterns of metastases will depend on the primary tumor. Certain tumors rarely metastasize, whereas some cancers tend to metastasize earlier than others. The presence of metastatic disease may also be correlated with the tumoral histology. Undifferentiated, anaplastic, and high-grade tumors have a tendency to generate more metastases than well-differentiated and low-grade tumors. The cells in a metastatic tumor resemble those in the primary tumor. However, when the metastatic tumor is undifferentiated, the pathologist can use several adjuvant techniques, such as immunohistochemistry, to try to identify the origin of the primary tumor. In rare cases, patients will have metastatic disease without a primary tumor found, and these patients are considered to have a cancer of an unknown primary tumor.

Clinical Presentation

Metastatic disease is usually present in late stages of the cancer. However, when metastases are present early in the course of the disease, the type and frequency of the symptoms will depend on the location and size of the metastatic lesions. For example, symptoms of liver impairment including development of jaundice and hepatomegaly can indicate that the cancer has spread to the liver, and neurological symptoms such as headaches and seizures may indicate the presence of brain metastases, whereas bone metastases usually present as bone pain.

Diagnosis

The diagnosis of metastatic disease is one of the most important steps in the staging of patients with cancer. The detection of metastatic disease has an important role on the prognosis and treatment of cancer patients. Several imaging modalities can be used in the assessment of presence of metastatic disease, including ultrasound (US), computed tomo-graphy (CT), magnetic resonance imaging (MRI) and 2-[ ¹⁸ F] fluoro-2-deoxy-D-glucose positron emission tomography (FDG-PET)/CT. Among them, US has advantages such as noninvasiveness, ready availability, and relatively low cost. CT scans of the chest, abdomen, and pelvis are the most common imaging methods used for the initial staging of oncologic patients, as CT is widely available and is a noninvasive diagnostic tool. MRI, a nonionizing imaging technique, is very helpful in patients who are allergic to iodinated contrast agents and has intrinsic multiplanar capabilities that offer increased sensitivity in the detection of metastatic disease due to high soft-tissue contrast resolution. PET and CT performed in a single scanning session (PET/CT) is used for staging of oncologic patients. FDG uptake is an important discriminating factor in the evaluation of potentially malignant cells. Additionally, newly developed PET radionuclides are being used to image neuroendocrine tumors and prostate cancer, among others. More recently, simultaneous PET and MRI (PET/MRI), which combines the anatomic and quantitative strengths of MRI with physiologic information obtained from PET, has been used for the detection and characterization of metastatic disease.

Treatment

Treatment for metastatic disease usually depends on several factors, including the size and location of the metastasis, the patient’s age and general health, and the types of treatments the patient has had in the past. Patients with single metastasis or single site of metastatic disease need to be evaluated for possible curative treatment, usually with surgical resection. However, when there are multiple metastases, systemic treatment such as chemotherapy, and in some cases radiation therapy and clinical trials or a combination of these, may be necessary. Recent exciting developments in cancer immunotherapy, which involves priming the host’s natural immune defenses to recognize, target, and destroy cancer cells effectively, and advances in targeted therapy have provided some hope in fighting metastatic disease.

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