The MastAttack 107: The Layperson’s Guide to Understanding Mast Cell Diseases, Part 83

96. Why are cancer drugs used to treat mast cell disease?

Disclaimer: The following post was written by me in my capacity as a subject matter expert in mast cell disease and author of MastAttack. This is not work product of my position as a Senior Scientist for a large research organization. All below statements are attributable directly to me in my role as author of MastAttack and are in no way attributable to my employer. Information presented here is publicly available and includes no confidential information learned in my capacity as a Senior Scientist for my employer.

  • There are a number of medications used to treat cancers that are also used to treat mast cell disease. Some of those medications are old school chemotherapies, some are newer, targeted chemotherapies, and some help to control the immune system.
  • In mastocytosis, the body makes too many mast cells. If the bone marrow makes way, way too many mast cells, and those mast cells don’t function correctly, the mast cells can act like cancer cells. This can cause the mastocytosis to behave like cancer.
  • Systemic mastocytosis has several subtypes. The least serious forms do not act like cancer.
  • Indolent systemic mastocytosis (ISM) is the least severe form of systemic mastocytosis. ISM has a normal lifespan. While patients with ISM are at risk of dying for anaphylaxis, an important distinction is that patients with ISM do not die because the mast cell disease acts like a cancer. ISM does not act like cancer.
  • Smoldering systemic mastocytosis (SSM) is a moderately serious form of systemic mastocytosis. SSM can shorten lifespan. In SSM, the body is starting to make lots more mast cells than it should. Those mast cells can affect how organs function. SSM acts like an early cancer.
  • SSM requires treatment to stop it from becoming a more serious form of mastocytosis called aggressive systemic mastocytosis (ASM) that acts like a serious cancer. The treatments used to manage SSM are also used in some cancer patients to help fight cancer. These include meds that affect your immune system, like interferon; newer targeted therapies and chemos, like tyrosine kinase inhibitors; and older chemo drugs, like cladribine.
  • Aggressive systemic mastocytosis (ASM) is a serious form of systemic mastocytosis. ASM shortens lifespan significantly. In ASM, the body makes way too many mast cells. The bone marrow churns out so many mast cells into the bloodstream and then the abnormal mast cells get stuffed into various organs. The mast cells cause organ damage and can cause organ failure. ASM is often referred to as being malignant because it behaves just like a cancer. It is also treated like a cancer.
  • As mentioned above, interferon is a therapy that can affect how the immune system works. Interferon is sometimes used for ASM but it is less commonly used in ASM than in SSM. ASM patients need more aggressive treatment. Newer targeted therapies like tyrosine kinase inhibitors and multitarget kinase inhibitors are frequently used in ASM. Some of these newer therapies are FDA approved for treating some ASM patients. Cladribine and hydroxyurea are still common treatments for ASM.
  • Mast cell leukemia (MCL) is the most serious form of systemic mastocytosis. MCL greatly reduces lifespan. MCL causes production of an unbelievable number of mast cells. There are so many mast cells that they cannot all get stuffed into organs like ASM. This means that while there are lots of mast cells in the organs in MCL patients, there are so many mast cells like that there are still tons of them in the bloodstream. This leads to rapid organ failure, leading to death. Mast cell leukemia is cancer. It is treated like cancer with newer therapies like tyrosine kinase inhibitors and multitarget kinase inhibitors, as well as hydroxyurea or cladribine in some cases. As in ASM, some of the newer therapies are FDA approved to treat mast cell leukemia.
  • Sometimes patients with systemic mastocytosis develop a second blood disorder. This is called systemic mastocytosis with associated hematologic disease. Sometimes this second blood disorder is a form of cancer, like chronic myeloid leukemia. In these instances, the other blood disorder would be treated using cancer medications.
  • Mast cell sarcoma (MCS) is a cancerous form of systemic mastocytosis. Patients with MCS rapidly develop MCL and are treated as described above.
  • None of the therapies I mentioned here are indicated for cutaneous mastocytosis. Cutaneous mastocytosis does not behave like a cancer and is not treated like one.
  • In recent years, two other forms of mast cell disease have been described: mast cell activation syndrome and monoclonal mast cell activation syndrome.
  • Monoclonal mast cell activation syndrome (MMAS) is often considered to be a “pre-SM”. It is treated like indolent systemic mastocytosis and does not behave like a cancer.
  • Mast cell activation syndrome (MCAS) is not know to be an early form of SM. Many people live with MCAS for decades without ever developing SM.
  • Despite the fact that mast cell activation syndrome, monoclonal mast cell activation syndrome, and indolent systemic mastocytosis do not behave like cancer, cancer therapies are sometimes used in these patients. They are used when other therapies have failed and their symptoms are still poorly controlled. Generally, they are used when persistent mast cell activation becomes life threatening. In some instances, they may be used when a patient’s symptoms are not life threatening but are very disabling and cause a poor quality of life. In these cases, the patient and their provider make the assessment that they are able to assume the risk of using these medications.
  • There is very little data on the use of chemo and targeted therapies in patients with MCAS, MMAS and ISM, and no cancer therapies are FDA approved for these conditions. However, use of cancer meds for nonmalignant conditions is not that unusual. It is pretty common in autoimmune disease where lower doses of chemotherapy drugs can be effective in controlling the disease. Basically, the idea is that if we know that these therapies help forms of mast cell disease that behave like cancers then it might help those forms that don’t act like cancer.
  • On a number of occasions, I have seen patients discussing the dangers around certain cancer meds that are sometimes used to treat mast cell disease. In particular, I have seen comments that newer targeted therapies “do not kill cells”, “cannot cause organ damage”, and are “harmless.” This is completely untrue. There are thousands of articles on the side effects and complications of all of the meds I have described here. None of them are harmless. Patients need to understand the risks associated with these therapies.
  • I would like to add a note about something sort of related. Xolair is an anti-IgE medication that is used by many mast cell patients. It is a subcutaneous injection and is administered in a healthcare setting. Patients are required to stay in the office for a little while after the shots are given to be sure that they don’t have a bad reaction. Because the patient is monitored in the office after the shot, the provider’s office will bill insurance for the observation period. The old billing code for this often comes up as “chemotherapy observation” because the same code was used for patients who needed monitoring after chemo. This means that patients may see “chemo” on the explanation of benefits from their insurance company. This does not mean that they received chemo. Xolair is NOT chemotherapy. It’s just a quirk of the medical billing. There is now a new code for post injection observation for meds that are not chemo but not everyone has caught up to it. Just figured I would mention this as people ask about it from time to time.