Panitumumab

Colorectal Cancer Treatment

Panitumumab is used to treat metastatic colorectal cancer, which is cancer of the colon or rectum that has spread to other organs. It is specifically designed for patients whose tumors are identified as "wild-type" RAS, meaning the cancer cells do not have certain mutations in the KRAS or NRAS genes.

Common Uses

• First-line therapy: It may be used as the initial treatment for metastatic colorectal cancer when combined with specific chemotherapy medications.
• Single-agent therapy: It can be used alone if previous chemotherapy treatments have not been successful or are no longer working.
• Combination therapy for specific mutations: It may be used in combination with other targeted medications for certain types of mutated colorectal cancer as determined by laboratory testing.

Because this medication is only effective for certain types of cancer, healthcare providers must perform a diagnostic test to confirm the genetic status of the tumor before starting treatment.

Targeting Cancer Cells

Panitumumab belongs to a class of medications known as monoclonal antibodies. These are laboratory-made proteins designed to recognize and attach to specific targets in the body. In the case of panitumumab, the target is the epidermal growth factor receptor (EGFR).

Blocking Growth Signals

EGFR is a protein found on the surface of both normal cells and certain types of cancer cells. When naturally occurring substances in the body bind to these receptors, they send signals that tell the cell to grow, multiply, and survive. Panitumumab works by:

• Binding to the receptor: The medication attaches itself to the EGFR on the surface of the cancer cells.
• Interfering with signals: By occupying the receptor, it prevents other growth-promoting proteins from attaching.
• Inhibiting cell growth: Without these growth signals, the cancer cells may stop dividing and eventually die.

The Role of Genetic Markers

The effectiveness of panitumumab depends on the genetic makeup of the tumor. It is primarily used for cancers that have a "wild-type" KRAS gene. If the KRAS gene is mutated, the cancer cell may continue to grow even if the EGFR is blocked, because the mutation provides an internal signal for the cell to keep dividing regardless of external triggers.

Common Side Effects

Many people receiving panitumumab experience skin-related issues. Other common side effects may include:

• Skin rash, acne, or dry and itchy skin
• Nail inflammation or infections (paronychia)
• Fatigue or unusual weakness
• Nausea, vomiting, or diarrhea
• Constipation or abdominal pain
• Loss of appetite and weight loss
• Mouth sores or inflammation
• Cough

Serious Side Effects

Some side effects can be severe and require immediate medical attention. Contact a healthcare provider if you experience:

• Severe skin reactions: Extensive blistering, peeling, or signs of skin infection such as warmth and swelling.
• Infusion reactions: Fever, chills, or breathing difficulties occurring during or shortly after the injection.
• Lung problems: New or worsening shortness of breath, wheezing, or a persistent cough.
• Eye issues: Redness, pain, swelling, or changes in vision.
• Electrolyte imbalances: Muscle spasms, shakiness, or irregular heartbeat, which may indicate low levels of magnesium, calcium, or potassium.
• Kidney issues: Decreased urination or swelling in the legs and feet, often associated with severe dehydration from diarrhea.

Dermatologic Toxicity

Panitumumab has a boxed warning for severe skin reactions. These reactions, which occur in the majority of patients, may include acne-like rashes, skin peeling, itching, and nail inflammation. In some cases, these conditions can lead to serious infections or life-threatening complications. Exposure to sunlight can worsen these reactions, and the use of sunscreen and hats is typically recommended.

Infusion Reactions

Severe infusion reactions can occur during or following the administration of panitumumab. Symptoms may include fever, chills, or difficulty breathing. If a severe or life-threatening reaction occurs, the medication is usually stopped permanently.

Lung and Eye Complications

• Interstitial Lung Disease (ILD): This medication has been associated with lung inflammation and scarring. If new or worsening respiratory symptoms such as cough or shortness of breath develop, treatment may be interrupted or discontinued.
• Ocular Toxicity: Serious eye problems, including keratitis (inflammation of the cornea) and corneal ulceration, have been reported. Prompt medical evaluation is necessary if eye pain or redness occurs.

Electrolyte Abnormalities

Panitumumab can cause significant decreases in magnesium, calcium, and potassium levels. Healthcare providers monitor these electrolyte levels through regular blood tests during treatment and for several weeks after the final dose is administered.

Genetic Testing Requirements

This medication is not indicated for patients whose colorectal tumors have certain mutations in the RAS genes (KRAS or NRAS). Evidence suggests that panitumumab is not effective in these cases and may lead to worse clinical outcomes. Genetic testing of the tumor is required before starting therapy.

Embryo-Fetal Toxicity

Based on its mechanism of action, panitumumab can cause harm to a developing fetus. Effective contraception is recommended for individuals of reproductive potential during treatment and for at least two months after the last dose. Breastfeeding is generally not recommended during treatment and for two months following the final dose.

Pregnancy

Panitumumab can cause harm to a developing fetus when administered to a pregnant woman. Animal studies have shown that the medication can lead to embryo-fetal toxicity and pregnancy loss. It is important to inform a healthcare provider if you are pregnant or planning to become pregnant before starting this treatment.

Individuals who can become pregnant should use effective contraception during treatment with panitumumab and for at least 2 months after the final dose. If a patient becomes pregnant while receiving this medication, they should be informed of the potential hazards to the fetus.

Breastfeeding

It is not known whether panitumumab passes into human breast milk. Because many drugs are excreted in human milk and there is a potential for serious adverse reactions in nursing infants, breastfeeding is not recommended during treatment. Healthcare providers typically advise waiting at least 2 months after the last dose of panitumumab before starting or resuming breastfeeding.

Fertility

Based on animal studies, panitumumab may impair fertility in females. The long-term effects on human fertility are not fully known, and patients should discuss these concerns with their medical team.

Available Forms

Panitumumab is supplied as a sterile, colorless, preservative-free liquid solution. It is intended for intravenous administration and must be prepared and given by a healthcare provider in a clinical setting.

• Intravenous Infusion: The medication is provided in single-dose vials. The solution is diluted into an infusion bag before being delivered directly into a vein.

FDA Approval Status

Panitumumab received its initial FDA approval in 2006. It is indicated for the treatment of patients with wild-type RAS (KRAS and NRAS) metastatic colorectal cancer. It may be used as a first-line treatment in combination with chemotherapy or as a single agent if previous treatments have failed.

Recent Regulatory Updates

In 2024, the FDA approved panitumumab for use in combination with sotorasib. This specific indication is for adult patients with KRAS G12C-mutated colorectal cancer that has progressed after receiving other types of chemotherapy.

Boxed Warning

The medication carries a Boxed Warning for dermatologic toxicity. Most patients experience skin-related side effects, which can be severe. These reactions may include rash, skin peeling, and infections. Healthcare providers are advised to monitor patients closely and may need to adjust or stop treatment if severe reactions occur.

Testing Requirements

Because panitumumab is only effective in tumors with specific genetic characteristics, the FDA requires the use of an approved diagnostic test to confirm a patient's RAS mutation status before treatment begins. The drug is not recommended for patients whose tumors have RAS mutations.

FDA Approval and Indications

Panitumumab was first approved by the U.S. Food and Drug Administration (FDA) in 2006. It is indicated for the treatment of patients with wild-type RAS metastatic colorectal cancer (mCRC). This includes patients whose tumors do not have mutations in the KRAS or NRAS genes.

The FDA has approved panitumumab for use in several clinical scenarios:

• As a first-line treatment combined with FOLFOX chemotherapy.
• As a single agent for patients whose cancer has progressed after receiving chemotherapy regimens containing fluoropyrimidine, oxaliplatin, and irinotecan.
• In combination with sotorasib for adult patients with KRAS G12C-mutated colorectal cancer who have already tried at least one other systemic therapy.

Regulatory Requirements and Warnings

The FDA requires the use of an FDA-approved test to confirm the absence of RAS mutations before starting panitumumab therapy. Clinical trials have shown that patients with RAS mutations do not benefit from this medication and may experience worse outcomes if it is used.

The FDA-approved labeling includes a Boxed Warning for dermatologic toxicity. This warning highlights the risk of severe skin reactions, such as dermatitis and cellulitis, which may lead to infectious complications. The FDA also monitors the drug for risks related to infusion reactions and lung disease.