Gefitinib, known by its brand name Iressa, is a medication used to treat certain cancers. It belongs to a category of drugs called targeted therapies, designed to specifically interfere with cancer cell growth and progression. This approach minimizes harm to healthy cells.
Mechanism of Action
Targeted therapies, like gefitinib, differ from traditional chemotherapy by focusing on specific molecules involved in cancer cell growth, rather than broadly attacking rapidly dividing cells. Many cancer cells have an overactive protein on their surface called the Epidermal Growth Factor Receptor (EGFR). This receptor normally helps cells grow and divide, but in some cancers, it can be mutated, leading to uncontrolled proliferation.
Gefitinib functions as a tyrosine kinase inhibitor (TKI), which means it specifically blocks the signaling activity of this faulty EGFR. It achieves this by binding to the adenosine triphosphate (ATP)-binding site within the EGFR’s intracellular domain, thereby preventing the receptor from activating downstream pathways that promote cell growth and survival.
Patient Eligibility
Gefitinib is primarily used to treat non-small cell lung cancer (NSCLC). Its effectiveness depends on the presence of specific genetic changes within the EGFR gene in the patient’s tumor. These mutations, such as deletions in exon 19 or a substitution at exon 21 (L858R), lead to the overactive EGFR that gefitinib targets.
Doctors determine patient eligibility by performing a biopsy. This sample is then analyzed to identify these particular EGFR gene mutations. If a patient’s cancer does not possess these specific mutations, gefitinib is not an effective treatment option.
Administration and Monitoring
Gefitinib is administered as an oral tablet, with the standard dosage being one tablet taken once daily. Patients can take this medication with or without food. Swallow the tablet whole with a glass of water; if swallowing is difficult, the tablet can be dissolved in half a glass of still water.
Doctors conduct regular check-ups to monitor the patient’s response. These include imaging scans, such as CT scans, performed every few months. Blood tests are also performed to monitor various health markers, including liver function.
Common and Serious Side Effects
Common side effects are generally manageable. These include skin reactions such as rash, acne-like breakouts, or dry skin, which can be alleviated with moisturizers or topical treatments. Diarrhea is also common, and anti-diarrhea medications can help manage this symptom.
Patients may also experience nausea, vomiting, and a decrease in appetite. These common side effects are usually not severe and can be managed with supportive care. Patients should discuss any side effects with their healthcare team to find appropriate management strategies.
More serious side effects can occur, requiring immediate medical attention. These include severe lung problems, such as interstitial lung disease, which can manifest as new or worsening shortness of breath or cough. Liver issues may also arise, indicated by symptoms like yellowing of the skin or eyes, or dark urine.
Gastrointestinal perforation, a hole in the stomach or intestine, can occur, causing severe abdominal pain. Serious eye problems, including dry eyes or corneal erosion, can develop. Patients should contact their doctor immediately if they experience any of these more severe symptoms.
Acquired Resistance
While gefitinib can be effective in treating EGFR-mutated non-small cell lung cancer, cancer cells can eventually adapt and develop mechanisms to bypass the drug’s effects. This phenomenon is known as acquired resistance, where the tumor begins to grow again despite ongoing treatment. This is a challenge with many targeted therapies, as cancer cells can evolve new mutations or activate alternative signaling pathways.
The development of resistance does not mean treatment options are exhausted. Doctors have other strategies available, which may include switching to a different type of targeted therapy, such as a next-generation tyrosine kinase inhibitor, or considering traditional chemotherapy or other approaches, depending on the specific resistance mechanism identified.