Solid Tumors vs. Blood Cancers

Most cancers form a solid mass called a tumor. That is a lump of abnormal cells you can often see on a scan. Blood cancers work differently. Instead of one lump, abnormal blood cells build up in the blood, bone marrow, or lymph system. Both are cancer. But they are found, staged, and treated in different ways.

A solid tumor grows in one place, at least at first. This could be the breast, lung, colon, or another organ. Doctors can often see it on imaging and measure it. They can describe exactly where it sits. Surgery to remove the tumor is often part of treatment, since there is a defined mass to take out. Staging for solid tumors usually looks at the tumor's size, and whether it has spread to nearby lymph nodes or distant organs.

Leukemia is a cancer of the blood and bone marrow. Bone marrow is the spongy tissue inside bones, where blood cells are made. In leukemia, the marrow makes too many abnormal white blood cells. These cells crowd out healthy blood cells. They do not form a lump you could point to on a scan.

Lymphoma is a cancer of the lymphatic system. This is the network of vessels and glands that helps fight infection. Abnormal lymphocytes, a type of white blood cell, build up in lymph nodes and lymphatic tissue. Lymphoma can sometimes cause a swollen lymph node that feels like a lump. But the disease itself is not confined to one spot, the way a solid tumor is.

Multiple myeloma is a cancer of plasma cells, another type of white blood cell. It is found mainly in the bone marrow. It can weaken bone in multiple places at once, instead of forming one central tumor.

Blood cancers do not form one measurable mass. So diagnosis relies heavily on blood tests, and on a bone marrow biopsy. That is a procedure that removes a small sample of marrow, usually from the hip bone, to study under a microscope. Staging for blood cancers often looks at blood cell counts, how much bone marrow is affected, and which lymph node areas are involved. It does not rely on a tumor's physical size the way solid tumor staging does.

Solid tumors are often treated with surgery to remove the tumor. Doctors sometimes add chemotherapy or radiation too. Blood cancers usually cannot be treated with surgery, since there is no single mass to cut out. Treatment instead relies on chemotherapy, targeted therapy, immunotherapy, or a stem cell transplant. A stem cell transplant replaces damaged bone marrow with healthy cells, often from a donor.

Understanding which category your cancer falls into helps explain your specific treatment plan. If your team is not recommending surgery, and you are wondering why, this is often the reason. There is no defined tumor to remove. Knowing this can make an unfamiliar treatment plan feel less confusing. It can also help you ask more useful questions at your next appointment.

If you have a blood cancer, expect blood counts to matter enormously throughout your care. Low white blood cells raise infection risk. Low red blood cells cause fatigue and can need a transfusion. Low platelets raise bleeding risk. Your team will check these often, sometimes weekly or more, especially during and right after treatment.

Ask whether your cancer is a solid tumor or a blood cancer, and how that shapes your options. Ask what tests are used to monitor your specific cancer. Ask why surgery is, or is not, part of your plan. Ask how often your blood counts will be checked, and what results would prompt a call to your team.

• National Cancer Institute — What Is Cancer?.