When a doctor recommends both a Positron Emission Tomography (PET) scan and a biopsy, it can lead to questions about why both are necessary. While both play distinct roles in medical diagnosis, they complement each other to provide a comprehensive understanding of a health condition.
How PET Scans Work
PET scans operate by detecting metabolic activity within the body’s tissues. Patients receive an injection of a small, safe amount of a radioactive tracer, commonly fluorodeoxyglucose (FDG), a sugar analog. As cells use glucose for energy, they absorb this tracer. Areas with higher metabolic rates, such as rapidly growing cells, accumulate more FDG and “light up” on the scan. This allows medical professionals to visualize areas of increased cellular activity that might indicate disease.
The scanner detects emitted radiation, creating images showing FDG accumulation. This functional imaging can highlight changes in tissues and organs often before structural changes are visible on other imaging tests. PET scans are useful for revealing areas with atypical metabolism, associated with various conditions including cancer, heart disease, and brain disorders.
How Biopsies Work
A biopsy is a medical procedure to obtain a tissue sample for microscopic examination. The sample is sent to a pathology laboratory, where a pathologist examines it. The purpose of a biopsy is to allow for a direct, cellular-level assessment of suspicious areas.
By directly visualizing the cells, pathologists determine their type, structure, and organization. This microscopic analysis helps identify if cells are diseased, such as cancerous or benign, or if they show signs of inflammation or infection. The information from a biopsy provides a definitive diagnosis that imaging alone cannot offer, forming a crucial step in understanding a patient’s condition.
Why PET Scans Aren’t Definitive
While PET scans are highly sensitive in detecting areas of increased metabolic activity, this activity is not exclusive to cancerous cells. Other conditions, such as inflammation, infection, or benign growths, can also exhibit elevated metabolic rates and absorb the FDG tracer, causing them to “light up” on the scan. These occurrences are often referred to as false positives, meaning the scan suggests a problem that is not cancer. For example, infectious processes like abscesses or inflammatory conditions such as sarcoidosis can show intense FDG uptake.
A PET scan provides functional information about how cells are behaving, but it does not reveal the precise cellular structure or type. Therefore, it cannot differentiate with certainty between a malignant tumor and a benign condition that also has high metabolic activity. To obtain a definitive diagnosis, a tissue sample is required for pathological confirmation. This direct examination is necessary to confirm the presence of cancer, determine its specific type, and guide appropriate treatment decisions.
After the Biopsy
Once the tissue sample is collected, it is sent to a pathology laboratory. There, the sample undergoes a series of processing steps, including preservation, embedding, and slicing into thin sections. These slices are mounted on glass slides and stained with special dyes to highlight cellular features, making them visible under a microscope.
A pathologist examines these slides to analyze the cells and tissues. The pathologist’s report provides a definitive diagnosis, detailing the type of cells present, whether they are cancerous or benign, and often provides additional information such as the grade or stage of cancer if detected. This report is communicated to the treating physician, who uses this information to develop a tailored treatment plan.