MAP chemotherapy is a combination of medications used to treat specific cancers, most frequently osteosarcoma, a type of bone cancer. It is often used after a tumor has been surgically removed. The name “MAP” is an acronym for the three drugs in the regimen, which work together to target cancerous cells throughout the body. The treatment is intensive and follows a structured schedule to maximize its effect while allowing the body periods of rest.
Components of the MAP Regimen
The “M” in MAP stands for Methotrexate, an antimetabolite drug. It interferes with the metabolic processes required for creating DNA. By blocking an enzyme involved in folate metabolism, Methotrexate halts the ability of cancer cells to replicate their genetic material and divide. In the MAP regimen, it is administered in very high doses to ensure it reaches and kills as many cancer cells as possible.
The “A” represents Adriamycin (the brand name for Doxorubicin), an anthracycline antibiotic. It works by inserting itself into the DNA of cancer cells and blocking an enzyme called topoisomerase II. This enzyme unwinds and rewinds DNA strands during replication. By inhibiting this process, Doxorubicin creates breaks in the DNA, which prevents cancer cells from dividing and leads to their death.
“P” signifies Platinol (the brand name for Cisplatin), a platinum-based drug. It acts by binding to the DNA of cancer cells, creating cross-links within the DNA strands that damage the genetic code. This damage disrupts the cell’s ability to repair its DNA. Unable to repair the damage or replicate, the cancer cell is triggered to self-destruct through a process called apoptosis.
Treatment Administration and Schedule
The MAP regimen is administered in a series of treatment cycles, providing a recovery period between drug applications. A full course of treatment involves multiple cycles spanning several months. Patients receive a set number of cycles before surgery to shrink the tumor, and more cycles after surgery to eliminate any remaining cancer cells.
All three drugs are delivered into the bloodstream through an intravenous (IV) line. The high-dose Methotrexate portion of the treatment requires a hospital stay. This allows for continuous IV hydration and close monitoring of drug levels in the blood. Doxorubicin and Cisplatin are administered together over one or two days and may be given in an outpatient clinic.
The sequence of drug administration is carefully planned to maximize the drugs’ effects while managing their impact on healthy tissues. Doxorubicin and Cisplatin are given at the beginning of a treatment week. The high-dose Methotrexate infusions are scheduled for later weeks within the same cycle.
Common Side Effects
MAP chemotherapy causes a range of side effects. Common effects include fatigue, nausea and vomiting, and hair loss (alopecia). The treatment also suppresses bone marrow activity, leading to low blood cell counts. This can result in a higher risk of infection from a shortage of white blood cells, and fatigue from a lack of red blood cells.
High-dose Methotrexate can cause mucositis, which is painful inflammation and sores in the mouth and digestive tract. It can also impact liver and kidney function, which requires careful monitoring.
Doxorubicin can cause damage to the heart muscle (cardiotoxicity), which can be an issue during treatment or a long-term complication. Cisplatin can cause kidney damage (nephrotoxicity) and hearing loss or ringing in the ears (ototoxicity). Another side effect of Cisplatin is nerve damage (neuropathy), causing tingling, numbness, or pain in the hands and feet.
Monitoring and Supportive Care During Treatment
Rigorous monitoring is used to manage the treatment’s impact. Frequent blood tests are performed to track blood cell counts, including white blood cells, red blood cells, and platelets. These tests also measure kidney and liver function to detect drug toxicity early. Specific tests are used to monitor for organ damage, such as echocardiograms to assess heart function and audiograms to check for hearing loss related to Cisplatin.
Supportive care is fundamental to preventing and managing side effects. Patients receive anti-nausea medications, and intravenous fluids are administered to maintain hydration and help flush drugs from the system. Medications like pegfilgrastim may also be given to boost white blood cell counts. A “rescue” drug called Leucovorin (folinic acid) is given starting 24 hours after a high-dose Methotrexate infusion. Leucovorin protects healthy cells from Methotrexate’s toxicity by providing them with a form of folic acid they can use. The dosage is carefully adjusted based on the level of Methotrexate remaining in the bloodstream.