Prolymphocytic leukemias (PLLs) are rare lymphoid leukemias, which account for only about 2% of all mature lymphoid leukemias. PLLs present like leukemia and, like lymphomas, they start in the lymphocytes, but do not form solid tumours. PLLs are also considered lymphoproliferative disorders, which mean that lymphocytes are produced in large amounts. PLLs were thought to be a rare variation of chronic lymphocytic leukemia (CLL), but are now considered a distinct disease.
PLL often occurs in older people, usually around the age of 65–70. It is slightly more common in men than in women. A person with PLL will usually have an enlarged spleen (splenomegaly) and a very high white blood cell count. Unlike other non-Hodgkin lymphomas (NHLs), the lymph nodes are not usually enlarged.
PLL is divided into 2 types based on the type of lymphocyte that the PLL starts in:
Both B-PLL and T-PLL behave fairly aggressively.
Although these 2 types of PLL share some of the same characteristics, the World Health Organization (WHO) classifies them as different types of lymphoid leukemias.
PLLs are difficult to treat. Treatment is similar to CLL.
People with PLL who do not have any symptoms and whose cancer does not seem to be progressing do not need treatment right away. They are watched and treatment is started if the PLL begins to cause symptoms or it looks like the cancer is progressing.
Chemotherapy drugs used to treat CLL are also used to treat PLL. Unlike CLL, chlorambucil (Leukeran) by itself is not usually effective for treating B-PLL or T-PLL. PLL responds better when combinations of chemotherapy drugs are used. These combinations produce responses, but they may not be long-lasting. Some combinations that may be used are:
Other chemotherapy drugs, called purine analogues, are often used to treat PLL and seem to be effective:
Monoclonal antibodies are a type of biological therapy that has been effective in treating certain types of NHL. These drugs may be used alone or in combination with chemotherapy to treat PLL.
Removing the spleen with surgery (splenectomy) or giving external beam radiation therapy to the spleen may be used in some people with PLL who have very enlarged spleens. These measures are used to relieve pain or to control symptoms (palliative therapy).
A stem cell transplant (SCT) is sometimes used to treat people with aggressive PLL. Many people with PLL are older or may not be in good health, so a SCT is often not a suitable option for them. However, it may be an effective option for younger people with PLL.