How do we know if treatment is working in patients dealing with solid tumors? Clinically, we like to see symptom improvement over time. If there is a tumor causing pain, swelling, obstruction, then over time we like to see improvement of these symptoms while on treatment. We like to see patients come off their nausea or pain meds. Biochemically, we can now assess circulating tumor DNA (ctDNA) which can be extremely helpful for folks who are on immunotherapy. Going from measurable ctDNA at baseline prior to starting therapy to undetectability is favorably prognostic sign for the long term. For most patients, we will assess the response with some sort of imaging. A CT scan or MRI of the specific body part is typically the “Kodak” picture we will use. See tumors at baseline and then see those tumors shrink over time or remain stable or progress? Occasionally, PET scan can be helpful if we want to assess a functional response. Meaning we inject radiographic glucose into the patient and see how much of a difference in glucose uptake the tumor has before and after treatment. Bone scans can be helpful for identifying new metastatic bone disease.
Not everyone needs every single test under the sun and most folks probably do not need a PET scan. There are potential false positives and false negatives that we must be careful about. Lung nodules are quite common with CT scans and most are benign. However, we may be more concerned about those nodules if these are new, enlarging, or have the typical appearance of malignancy. A lot of folks think the PET scan is the ultimate test for ruling out cancer and it is very possible to have metastatic disease and a negative PET. Or in other words a FALSE-NEGATIVE scan! For example, certain low-grade cancers and small tumors will not light up on the PET scan. Or vice versa, you can have a FALSE-POSITIVE finding meaning seeing something lights up but have nothing to do with cancer? FDG PETs are sugar or glucose scans and wherever the sugar accumulates, that will “glow or light up” the scan and the radiologist will have to say “cannot rule out cancer”? We often have to remind patients and their families that infection and inflammation can also “light up” the scans.
When a patient is diagnosed with cancer, one of the important things that their healthcare team will do is to determine the best way to assess the response to treatment. One way to do this is through imaging tests, which can help us see how the cancer is responding to treatment.
MRI: Magnetic Resonance Imaging (MRI)
Is a non-invasive imaging technique that uses a magnetic field and radio waves to produce detailed images of the body. It is often used to evaluate soft tissue structures, such as the brain, spinal cord, and joints. An MRI can help us see how the tumor is responding to treatment by showing changes in the size and shape of the tumor. MRI scan is best scan typically for the liver, brain, spine, extremities.
CT Scan: A Computed Tomography (CT) scan
Is a non-invasive imaging technique that uses X-rays to produce detailed cross-sectional images of the body. It is often used to evaluate organs such as the lungs, liver, and kidneys. A CT scan can help us see how the tumor is responding to treatment by showing changes in the size, shape, and density of the tumor. These imaging are the workhorse for most oncologist. Easy, quick, reliable pictures especially with contrast. The drawback is a dose of radiation so we do not like to do too many in a short period of time.
PET Scan: A Positron Emission Tomography (PET) scan
Is an imaging technique that uses a radioactive tracer to visualize metabolic activity in the body. It can help us see how the tumor is responding to treatment by showing changes in the metabolic activity of the tumor. There are different “paints” for different disease types. For example, using FDG PET is a common scan we use for most cancers with the intent of staging or assessing response. Other types of “paints” we use are dotatate PET used for metastatic neuroendocrine tumors or PMSA PET for prostrate cancers.
Nuclear Scans
Nuclear medicine imaging uses small amounts of radioactive material to diagnose and treat a variety of diseases. A nuclear scan can help us see how the tumor is responding to treatment by showing changes in the distribution and uptake of the radioactive material in the tumor. Bone scans are used for assessing metastatic disease to the bones.
Understanding the different types of imaging tests used in oncology to assess response can be helpful in understanding how the cancer is responding to treatment. It is important for patients to discuss with their healthcare team which imaging test is best for them, as each test has its own advantages and disadvantages. By working together with their healthcare team, patients can gain a better understanding of their cancer and the best way to monitor their response to treatment.
About the author
Dr. Sajeve Thomas is a distinguished medical professional and a compassionate guide in the field of oncology. With over a decade of dedicated experience as a board-certified medical oncologist/internal medicine specialist, Dr. Thomas has become a trusted expert in the treatment of melanoma, sarcoma, and gastrointestinal conditions. Currently practicing at the renowned Orlando Health Cancer Institute, he brings a wealth of expertise to the complex and challenging world of oncology.