MGMTd has also been described to occur by promoter rearrangement. In cells with MGMTd, DNA damage by TMZ activates the next stage of repair in cells with a proficient Mismatch Repair enzyme complex (MMRp). In MMRp the MMR protein complex identifies the damage and causes cells to arrest and undergo death which inhibits tumor growth. However, if cells have combined MGMTd and MMR deficiency (MGMTd + MMRd) then cells retain the induced mutations and continue to cycle and are resistant to effects of TMZ. In gliomas and other cancers MMRd has now been reported to occur as primary MMRd (intrinsic or germline Lynch bMMRd) or as secondary MMRd (acquired - not present in the original untreated tumor). The latter occurs after effective treatment and cytoreduction of tumors with TMZ and then selection or induction of mutant MSH6, MSH2, MLH1, or PMS2 proteins and cells which are MMRd and TMZ resistant. The latter is described as an acquired resistance pathway with hotspot mutations in glioma patients (MSH6 p.T1219I). Other resistance pathways are also likely to exist. References
Further reading
External links
"Temozolomide". Drug Information Portal. U.S. National Library of Medicine. "Temozolomide (Temodal)". Cancer Research UK.
The hormonal and intellectual deficits created by these therapies causes significant impairment of the survivors.In current clinical studies, the patients are divided into low-, standard- and high-risk groups:

Depending on the study, healing rates of up to 100% are achieved in the low-risk group (usually WNT-activated). The current efforts are therefore moving in the direction of reducing the intensity of the therapy and thus the negative long-term consequences while confirming the high healing rates. In the HIT-SIOP PNET 4 study, in which 340 children and adolescents of the standard-risk group between the ages of four and 21 from several European countries participated, the 5-year survival rate was between 85% and 87% depending on the randomization. Around 78% of the patients remained without relapse for 5 years and are therefore considered to be cured. After a relapse, the prognosis was very poor. Despite intensive treatment, only four of 66 patients were still alive 5 years after a relapse. A US study involved 161 patients between the ages of three and 21 with a high-risk profile. Depending on the randomization, half of the patients additionally received carboplatin daily during the radiation. The 5-year survival rate of patients with carboplatin was 82%, those without 68%. The European SIOP PNET 5 study is currently taking place and will run until April 2024, in which an attempt is made to confirm the promising results with carboplatin during irradiation in the standard risk group. Epidemiology
Medulloblastomas affect just under two people per million per year, and affect children 10 times more than adults.