What is a Malignant Rhabdoid Tumor?

If your child was diagnosed with MRT you probably know some or all of this. I just wanted to put this information in one place for oncofamilies new to the diagnosis, and their extended family and friends.


Rare cells with rhabdoid features Image source: Atypical Teratoid/Rhabdoid Tumor of the Spine, American Journal of Neuroradiology, March 2007

Malignant rhabdoid tumor is a rare childhood cancer, with only 20-25 cases occurring in the United States each year. Within the United Kingdom the age-standardized annual incidence is 1 in 2,000,000. The majority of cases are in children under two years old, and are most commonly diagnosed at 15 months, but can occur from birth and, although very rare, can be found in adults. The most common place MRT occurs is in the kidneys, but can be found in any soft tissue (in the brain it is called atypical teratoid rhabdoid tumor AT/RT). Tumors outside of the kidneys are generally referred to as extrarenal malignant rhabdoid tumors.  The diagnosis of MRT is generally done via genetic testing of the tumor. Almost all rhabdoid tumors are missing or have a mutation in SMRCB1 (also known as INI1, SNF5, BAF47 or mSWI/SNF). SMRCB1 is a tumor suppressor gene. Tumor suppressor genes have a repressive effect on cell growth and promote apoptosis, or programmed cell death. This means cells which are missing or have mutations in these genes can no longer repress tumors, or keep cell growth in check. If you are told your child's MRT is INI1 negative , it means that the tumor supressor gene is missing. The genetic testing done on the tumor can only tell you about the cells of the tumor itself, further genetic testing is needed to determine if the patient has a germline mutation or if the mutation was somatic. When a germline mutation is present it means that the mutation is in every cell and that it can be inherited, while a somatic mutation is limited to the cells that divided from the original mutated cell and is not hereditary. If a germline mutation is found, the parents of the patient will be tested to see if the condition was inherited or if it is spontaneous mutation. A spontaneous germline mutation means they are the first to have the mutation and that they could pass it to their offspring. A germline mutation in SMARCB1 or SMARCA4 would mean that the patient has Rhabdoid Predisposition Syndrome (RPS). A mutation or gene deletion in SMARCB1 is called Rhabdoid Predisposition Syndrome Type 1, and in SMARCA4 it is Type 2. If a person has Rhabdoid Predisposition Syndrome, they have a 30% chance of developing a tumor. There is a 50% chance that RPS would be passed to their children if the other parent did not have RPS as well. (Statistics are currently only available for Type 1, as Type 2 is very rare and there is not a large enough sample size.) Knowing if you or your child has a predisposition syndrome is important for future screening and possibly family planning. If RPS is present it will most likely affect the frequency and types of scans. For example, a patient with MRT of liver without RPS may receive MRIs of the abdomen twice a year, but the same patient with RPS may receive MRIs of the abdomen and brain four times a year. Likewise, if the patient's parent or sibiling has RPS, but has not developed a tumor, it is important for their doctor to be aware of the predisposition so that they can be more diligent during well visits, or educated about the symptoms of tumors. The most common treatments for MRT are surgery, and frontline chemotherapy; radiation is sometimes also used. Removing the tumor, called a tumor resection, is generally the first step followed by chemotherapy. If the tumor is not able to be removed completely or is inoperable chemo may be given first in an attempt to shrink the tumor or kill the affected cells. Multiple resections may be needed. In some cases, such as an inoperable liver tumor, the patient may need an organ transplant. Chemotherapy is received by almost all MRT patients, even in cases where the tumor is removed in its entirety. Chemotherapy drugs are intercellular poisions which inhibit cell division and growth. The drugs or agents are given intraveniously and treat cancer throughout the body, rather then in a specific location (like radiation therapy). The most commonly used chemotherapy agents are cyclophosphamide, cisplatindoxorubicin,  etoposidevincristinecarboplatin, and ifosfamide.  Chemotherapy can result in serious and long term side effects in children, such as hearing loss, fertility loss, developmental delays, heart problems and secondary cancers.The side effects of chemo are largely due to agents damaging cells that divide rapidly, such as bone marrow, cells in the digestive system and hair follicles. Damage to the bone marrow causes a reduced immune response, which can lead to more frequent infection and the inability to fight viruses and bacteria. It is important to follow the chemotherapy protocols given to you by the oncologist to protect your child. This may include limited exposure to crowds, dietary restrictions, no fresh flowers, certain hygiene routines, and more. MRT is a very aggressive cancer, and although the side effects of chemotherapy are serious, it is currently the best weapon we have in the battle for our children's lives. As your child's advocate, it is within your rights to ask doctors as many questions as you need to understand their disease, treatment, recovery and survivorship. It is within your rights to ask for a second opinion, or to seek care at a hospital you feel is better equipped to deal MRT. If your child has a MRT, or any cancer diagnosis, you will have to make many difficult decisions about their care. Please be kind to yourself. It is overwhelming, but can be managed one task at a time and one day at a time. Remember that there is large community of oncofamilies who know how you feel and care about you and your child. Seek help when you need it, from your oncology team, family, mental health professionals, and the larger onco-community. You are not alone.

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