What Is Panitumumab (Vectibix)? FDA Approval, Licensing and Reimbursement in Turkey

• FDA Approved: Yes (Initial approval date: September 27, 2006)
• Brand Name: Vectibix
• Active Ingredient: Panitumumab
• Route of Administration: Intravenous
• Class: Monoclonal antibody, anti-EGFR antibody
• Category: Targeted agent
• Manufacturer: Amgen
• Distribution in Turkey: Amgen
• Approved Cancers: FDA-approved for metastatic colorectal cancer (mCRC)

What Is Vectibix?

Vectibix, containing the active ingredient panitumumab, is a fully human IgG2 monoclonal antibody that binds to the epidermal growth factor receptor (EGFR) to inhibit cell proliferation and cancer cell survival.

What Does Wild-Type RAS Mean?

Wild-type RAS refers to the natural, normal form of the RAS gene without genetic mutations. RAS genes control important signaling pathways that regulate cell growth and division. Mutated RAS genes, however, commonly play a role in cancer development, and their mutated forms are frequently found in cancer cells. Because wild-type RAS has no mutation, it may be more sensitive to certain cancer treatments, such as anti-EGFR therapies. Whether RAS is wild-type or mutant is therefore an important criterion in treatment selection.

How Does It Work?

• Panitumumab binds to EGFR (epidermal growth factor receptor) approximately 40 times more strongly than normal ligands, suppressing EGFR signaling and preventing cancer cell growth.
• Suppressing the EGFR signaling pathway stops important signals involved in cancer spread, including those governing cell proliferation, growth, invasive ability (invasion/metastasis) and blood vessel formation (angiogenesis).
• Panitumumab may increase the response to chemotherapy and/or radiation therapy, supporting the treatment process.
• Unlike certain other EGFR inhibitors, such as cetuximab , panitumumab's antitumor activity does not involve immunologic (immune-system-mediated) mechanisms.
• By inhibiting EGFR signaling, it may promote cell death (apoptosis) and control cancer cell proliferation more effectively.

FDA (US Food and Drug Administration) Approval History

• September 27, 2006 – The FDA approved Vectibix (panitumumab) to treat patients with metastatic colorectal cancer.
• May 23, 2014 – The FDA approved Vectibix with FOLFOX as first-line treatment for patients with KRAS wild-type metastatic colorectal cancer.
• June 29, 2017 – The FDA approved Vectibix (panitumumab) for patients with RAS wild-type metastatic colorectal cancer.
• January 16, 2025 – The FDA approved sotorasib and panitumumab for KRAS G12C-mutated metastatic colorectal cancer.

Licensing in Turkey

In patients who have not previously received panitumumab or other anti-EGFR therapies and have an ECOG performance score of 0-1, panitumumab is indicated for RAS wild-type metastatic colorectal cancer as first- or second-line treatment with only one of the FOLFOX or FOLFIRI combination chemotherapy regimens, until progression. If progression occurs or the accompanying chemotherapy regimen changes, panitumumab or another anti-EGFR therapy may not be used.

EGFR = epidermal growth factor receptor

RAS (KRAS and NRAS) = KRAS (Kirsten rat sarcoma 2 viral oncogene homolog) and NRAS (neuroblastoma RAS viral oncogene homolog)

ECOG = Eastern Cooperative Oncology Group

Is Vectibix Reimbursed in Turkey?

Panitumumab is covered by SGK reimbursement for patients with RAS wild-type metastatic colorectal cancer who have not previously received panitumumab or other anti-EGFR therapies and have an ECOG performance score of 0-1, as first- or second-line treatment with only one of the FOLFOX or FOLFIRI combination chemotherapy regimens, until progression.

Price: As of December 2025, pharmacy retail prices are as follows:

• VECTIBIX 20 MG/ML, 5 ML VIAL CONTAINING SOLUTION FOR INFUSION (1 VIAL) 20014.43 TL.
• VECTIBIX 20 MG/ML, 20 ML VIAL CONTAINING SOLUTION FOR INFUSION (1 VIAL) 79473.93 TL.

Mechanisms of Resistance

• Mutations in EGFR can reduce its binding affinity for panitumumab, leading to drug resistance.
• Reduced expression of EGFR on the cell surface may decrease panitumumab's efficacy and increase resistance.
• Mutations in the KRAS gene, particularly at codons 12 and 13, are an important factor in resistance to panitumumab.
• BRAF mutations may also contribute to panitumumab resistance by affecting the EGFR signaling pathway.
• NRAS mutations may contribute to panitumumab resistance by altering cellular signaling pathways.
• An increase in HER2 through gene amplification may activate alternative cellular signaling pathways, causing resistance to panitumumab.
• Increased HER3 expression may increase resistance by allowing cell growth signals to be transmitted through alternative pathways.
• Activation of alternative cellular signaling pathways, such as PI3K/Akt and IGF-1R, may reduce panitumumab's efficacy and cause resistance.
• Increased expression of the lncRNA MIR100HG and its embedded miRNAs (miR-100 and miR-125) may activate the Wnt signaling pathway, causing resistance to panitumumab.

Absorption

Panitumumab is administered by intravenous (IV) infusion and therefore has no oral bioavailability. Because it is delivered directly into the bloodstream, absorption is unlike that of oral drugs.

Distribution

Panitumumab's distribution in the body has not been fully characterized. However, pharmacokinetic studies report an average antibody half-life of approximately 6-7 days and dose-dependent saturation.

Metabolism

Panitumumab's metabolism has not been comprehensively described. Pharmacokinetic studies show saturation at a weekly dose of 2 mg/kg. Its half-life is approximately 6-7 days.

Dose Range

• The recommended dose for metastatic colorectal cancer (mCRC) is 6 mg/kg IV every two weeks.
• An alternative regimen is 2.5 mg/kg IV weekly.

Drug Interactions

No formal drug interaction has been identified for panitumumab.

Precautions

• Infusion reactions are less common than with cetuximab because panitumumab is a fully human antibody.
• EGFR expression levels do not predict clinical efficacy, so EGFR testing is not mandatory for clinical use of panitumumab.
• KRAS and NRAS testing must be performed. Only patients whose tumors have wild-type (nonmutated) KRAS and NRAS genes should be treated with panitumumab.
• Skin side effects are considered an indicator of panitumumab's effect. Skin reactions should therefore be monitored.
• It should be used with caution in patients with a history of lung disease (ILD) because they are at risk of worsening ILD.
• Patients who develop a skin rash are advised to protect themselves from the sun; this is covered by a black-box (high-risk) warning.
• Electrolyte levels (particularly magnesium and calcium) should be monitored during treatment and for at least 8 weeks afterward.
• It may harm the fetus; women of childbearing potential are therefore advised to use effective contraception during and after treatment.

Side Effects

1. Pruritus, dry skin and a pustular, acneiform rash on the face and upper torso. Skin toxicity may occur in up to 90% of patients.
2. Infusion-related symptoms (fever, chills, urticaria).
3. Increased cough, dyspnea and development of lung disease.
4. Hypomagnesemia.
5. Diarrhea.
6. Asthenia and general weakness (in 10-15%).
7. Inflammation and swelling of the nail beds occur with prolonged use.