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The 4 Main Types of Leukemia—Plus, Several Rare Types to Know

In 2021, the American Cancer Society (ACS) predicts there will be 61,090 new cases of leukemia, a type of cancer that affects the early blood-forming cells in the body. Most often, leukemia is a cancer of white blood cells (the prefix "leuk" actually means white), but other blood cells, like red blood cells and platelets, can be affected too.

These abnormal, immature blood cells essentially begin overcrowding the other, healthy blood cells—that leads to many of the telltale symptoms of leukemia, including chronic fatigue and weakness, unintentional weight loss, and increased infections.

What Are the Different Types of Leukemia? What Are the Different Types of Leukemia? comes back abnormal, and you might not even need treatment right away. "It kind of rumbles along," Jeffrey Schriber, MD, director of Hematologic Malignancies at Cancer Treatment Centers of America in Phoenix, tells Health.

The second main type of leukemia—acute leukemia—is faster growing and usually requires prompt treatment. People who have it may feel exhausted, lose weight without trying to, or develop random fevers. They might also bruise or bleed more easily than normal.

Determining whether leukemia is chronic or acute, however, is just one step in the diagnostic process. Within each of these broad groups are several subtypes, and getting diagnosed with a correct, specific type of leukemia is key to getting proper care. Here's a closer look at the four main types of leukemia, as well as some rare types to be aware of.

RELATED: What Are the Symptoms of Leukemia? 10 Signs to See Your Doctor

What are the main types of leukemia?

There are four types of leukemia diagnosed most frequently. Each one is either acute or chronic and affects a specific type of cell. They include: acute lymphocytic leukemia (ALL), acute myeloid leukemia (AML), chronic lymphocytic leukemia (CLL), and chronic myeloid leukemia (CML). Here's what to know about each type.

Acute lymphocytic leukemia

Also called acute lymphoblastic leukemia, ALL is the most common type of leukemia in children, though adults can get it as well, according to the ACS. The "acute" part of ALL means this type of leukemia progresses quickly—the ACS says that if it were to go untreated, ALL can be fatal in just a few months.

ALL specifically impacts lymphocytes, a special type of white blood cell that fights infection, per the US National Library of Medicine (MedlinePlus). With ALL, the body's bone marrow makes too many of abnormal lymphocytes, which crowd out healthy blood cells, causing symptom like increased infections, easy bruising or bleeding, and anemia.

It's not entirely clear what causes ALL, though it does have a genetic component; but the Mayo Clinic says previous cancer treatments, radiation exposure, and genetic disorders like Down syndrome are all risk factors for the disease.

As far as treatment goes, the regimen for ALL usually includes chemotherapy, radiation, stem cell transplantation, targeted therapy, or a combination of those, per MedlinePlus. Treatment is also usually split up into two phases: remission induction therapy, to kill leukemia cells and put the person in remission; and post-remission therapy, to keep the cancer from returning. According to the Leukemia and Lymphoma Society (LLS), nearly 90% of adults with ALL will reach remission—though relapse does happen in 20%–40% of patients.

Acute myeloid leukemia

Acute myeloid leukemia has quite a few different names: acute myelocytic leukemia, acute myelogenous leukemia, acute granulocytic leukemia, and acute non-lymphocytic leukemia, according to the ACS. It's one of the more common types of leukemia in adults, as risk increases with age, though some children can develop it as well.

This type of leukemia impact the myeloid stem cells in the bone marrow—the ones that go on to become healthy red and white blood cells, as well as platelets. But in AML, those myeloid cells don't mature; instead, they usually become an immature type of white blood cell called myeloblasts, according to the National Cancer Institute (NCI). There can also be an abnormal amount of immature red blood cells or platelets, called leukemia cells. When these abnormal cells build up, they make less room for other, healthier cells—again, causing infection, easy bleeding, or anemia, per the NCI.

AML also has a genetic component, though experts aren't clear what that is yet. The disease has a few different risk factors, including being a male of an older age, having a history of chemotherapy or radiation therapy, treatment for ALL as a child, exposure to benzene, and a history of a blood disorder called myelodysplastic syndrome, MedlinePlus says.

Treatment for AML is similar to that for ALL—chemotherapy, radiation therapy, chemo with stem cell transplantation, targeted therapy, or other drug therapy, the NCI says. It's also treated with remission induction and post-remission therapy. Per the ACS, two-thirds of AML patients who undergo chemotherapy reach remission.

RELATED: What Is Acute Lymphoblastic Leukemia? What to Know About This Blood Cancer

Chronic lymphocytic leukemia

Much like ALL, chronic lymphocytic leukemia is another type of leukemia that affects the lymphocytes, or white blood cells that help fight against infection, per MedlinePlus. With CLL, however, the leukemia is slow-growing (hence the term "chronic" attached to it). It's one of the most common types of leukemia in adults, normally occurring during or after middle age; it's rare in children.

CLL doesn't typically cause symptoms in the beginning—but later on in the course of the disease, when abnormal white blood cells begin to crowd out out other healthy cells in larger quantities, people can feel weakness or fatigue, being losing weight without an explanation, start bruising or bleeding easily, or have enlarged lymph nodes in the neck, armpit, stomach, or groin, MedlinePlus says.

Because CLL is often slow-growing, doctors sometimes take a "watchful waiting" approach to treatment, meaning they will closely monitor the patient until symptoms begin to worsen or change, per the NCI. If treatment is deemed necessary, it can include: chemotherapy, targeted therapy, radiation therapy, immunotherapy, or chemotherapy with either a bone marrow or peripheral stem cell transplant. Those diagnosed with CLL have a relatively good prognosis—according to the NCI, those with CLL have a relative five-year survival rate of 87.2%, meaning 87.2% of people diagnosed with CLL in a study group were still alive five years after their diagnosis.

Chronic myeloid leukemia

Chronic myeloid leukemia, sometimes known as  chronic myelogenous leukemia, is one of the rarer types of leukemia—only about 15% of leukemias in adults are CML, according to the ACS. Much like AML, CML is another type of leukemia that impacts the myeloid cells in the bone marrow; but, like CLL, it's a slower-growing kind of leukemia—but it can turn into a faster-growing kind of leukemia that becomes difficult to treat.

While the other most common types of leukemia don't have a known cause, most people with CML have a specific gene mutation called the "Philadelphia chromosome," per the NCI. This change results in person's bone marrow making a specific protein called tyrosine kinase, which causes too many stem cells to become white blood cells—and, as with other types of leukemia, those extra abnormal blood cells build up, leaving less room for healthy blood cells.

The treatment regimen for CML is similar to other forms of leukemia: targeted therapy, chemotherapy, radiation therapy, and chemotherapy with stem cell transplantation. But there are two other options as well: something called "donor lymphocyte infusion" (DLI), in which a donor's lymphocytes specifically are frozen and then thawed and given to the patient; and surgery in the form of a splenectomy, to remove the patient's spleen (which is essentially a large lymph node). The prognosis for CML seems good: the ACS says that most patients who have been treated with "highly-effective" drugs for CML—which came out in 2001—are still alive.

RELATED: After Recovering From Leukemia, She's Racing Marathons for a Cure

What are the rarer types of leukemia?

Although the above-mentioned forms of this blood cancer are more common, some people are diagnosed with one of the rarer types of leukemia. Those can typically include, but aren't limited to:

  • Hairy cell leukemia (HCL): The strange name of this type of leukemia is a nod to the fact that the cancer cells look like they have tiny hairs when examined under a microscope. People with hairy cell leukemia often have an enlarged spleen.
  • Chronic myelomonocytic leukemia (CMML): There are only about 1,100 cases a year of this blood cancer, according to the LLS. It has features of two other types of leukemia (myelodysplastic syndrome and myeloproliferative neoplasm), so it's also referred to as myelodysplastic/myeloproliferative neoplasm, the ACS says.
  • Juvenile myelomonocytic leukemia (JMML): Similar to CMML, except this rare type of leukemia is diagnosed in kids (usually infants and toddlers), per the LLS.
  • Large granular lymphocytic leukemia: There are two types of this rare leukemia, which is characterized by enlarged lymphocytes with granules that are easily visible under a microscope: T-cell type (T-LGL) and natural killer cell type (NK-LGL), according to Johns Hopkins Medicine. Either version may be acute or chronic.
  • Blastic plasmacytoid dendritic cell neoplasm (BPDCN): Formerly called natural killer cell leukemia/lymphoma, per the LLS, BPDCN is a rare combination of leukemia and lymphoma. (Leukemia and lymphoma are both blood cancers, but lymphoma mostly impacts the lymph nodes instead of the bone marrow.)
  • B-cell prolymphocytic leukemia (B-PLL): One of the rare and aggressive types of leukemia, B-PLL involves overproduction of a type of lymphocyte called B-cells. It can be difficult to diagnose and treat, per the LLS.
  • T-cell prolymphocytic leukemia (T-PLL): This type of leukemia is similar to B-PLL, except there's an overproduction of T-cell lymphocytes instead of B-cells, the LLS says. T-cells kill viruses whereas B-cells come in after the attack and produce antibodies.

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