Metastasis (mets) is the process by which cancer cells break away from the original tumor site and travel through the bloodstream or lymphatic system to form new tumors in distant organs. This spread signifies a more advanced stage of cancer, and finding these secondary tumors is necessary for determining treatment options and prognosis. Doctors employ a combination of patient observation, advanced scanning technologies, and cellular analysis to accurately detect and locate these secondary growths. These methods identify both the physical location of the lesions and the specific cellular composition of the disease.
Recognizing the Signs of Metastasis
A doctor’s initial suspicion of metastatic disease often begins with a patient reporting new or persistent, non-specific symptoms that suggest the cancer is progressing. These clinical indicators can include general signs of illness, such as unexplained weight loss or profound fatigue that does not improve with rest. Generalized symptoms prompt further investigation because they can be the first clue that cancer is growing or spreading.
More specific symptoms often relate directly to the organ where the cancer may have settled. For instance, new or worsening pain in the back, hips, or legs may suggest bone metastasis, while a persistent cough or shortness of breath could indicate tumors in the lungs. If the cancer has spread to the brain, a patient might experience chronic headaches, seizures, or changes in vision, balance, or speech. Jaundice, a yellowing of the skin and eyes, is a sign that the cancer may have established lesions in the liver.
Advanced Imaging Tools
Once clinical suspicion is raised, doctors rely on advanced medical imaging to physically locate the metastatic lesions throughout the body. These tools provide anatomical and functional maps that reveal where the cancer is hiding.
Computed Tomography (CT)
Computed Tomography (CT) scans use a series of X-ray images taken from multiple angles to create detailed, cross-sectional “slices” of the body. CT is effective for surveying large areas of the chest, abdomen, and pelvis, making it a routine tool for detecting metastases in organs like the liver, lungs, and lymph nodes. Often, an iodine-based contrast agent is injected to highlight blood vessels and make abnormal tissue densities, such as tumors, stand out more clearly.
Magnetic Resonance Imaging (MRI)
Magnetic Resonance Imaging (MRI) is preferred for visualizing soft tissues and areas that require fine detail, particularly the brain and spinal cord. MRI uses powerful magnetic fields and radio waves, rather than ionizing radiation, to generate highly detailed images. The technique offers superior contrast between different types of soft tissue, which is invaluable for identifying small, subtle lesions.
Positron Emission Tomography (PET)
Positron Emission Tomography (PET) scans provide a functional image by measuring metabolic activity within the body. Before the scan, a patient is injected with a radioactive sugar analog called fluorodeoxyglucose (FDG). Cancer cells consume glucose at a much higher rate than most normal cells. The FDG accumulates in these metabolically active tumor cells, causing them to “light up” on the PET scan.
PET scans are almost always performed in combination with a CT scan, creating a hybrid PET-CT image. This combination is effective because the PET portion shows the location of metabolic activity, while the CT portion provides the precise anatomical context of the lesion. By fusing the functional and structural data, doctors can accurately pinpoint small or widespread tumors.
Confirming the Diagnosis
While imaging studies can strongly suggest metastatic cancer, the definitive diagnosis requires obtaining a sample of the abnormal tissue for analysis. This involves a biopsy, where a small piece of the suspected metastatic lesion is removed, often using a needle guided by CT or ultrasound imaging. A pathologist then examines the cells under a microscope to confirm they are cancerous and determine their exact origin.
The pathology report verifies that the secondary tumor cells are genetically and morphologically identical to the original primary tumor, such as breast cancer cells found in a lung lesion. This confirmation ensures the patient receives treatment appropriate for the primary cancer type. Analyzing the tissue also allows for molecular profiling, which identifies specific genetic mutations or protein markers that can guide targeted therapies.
A modern, less invasive method for confirming the diagnosis is the liquid biopsy, which analyzes blood for circulating tumor DNA (ctDNA). As tumor cells die, they release fragments of their DNA into the bloodstream, which can be collected and analyzed. This non-invasive test offers a real-time snapshot of the entire disease burden, including the genetic makeup of multiple metastatic sites. This can be helpful for tracking disease progression and detecting new resistance mutations.