Up to 60% of patients with metastatic colorectal cancer can be treated with one of monoclonal antibodies targeted against epidermal growth factor receptor (EGFR). This treatment is associated with a specific spectrum of toxicity: acne-like rash from limited up to erythema, often with severe pruritus, sometimes combined with other types of skin toxicities (hair and nail changes). Previously in STEPP study investigators shown that pre-emptive treatment with oral doxycycline (200 mg daily), topical steroids and sun blockers reduces the number of more severe skin side effects of panitumumab.

The study is designed to described the profile of skin toxicity of EGFR blocking drugs combined with low-dose doxycycline (100 mg daily) used in the pre-emptive manner.

Patients with metastatic colorectal cancer treated with cetuximab or panitumumab usually develop the skin toxicity which can impair patients' quality of life as well as limit the treatment. We designed this trial to assess the effect of simplified protocol of pre-emptive treatment on the observed skin toxicities during cetuximab and panitumumab treatment of colorectal cancer.

The study is a cohort observational, single center study which should result in estimation of particular types of toxicities, especially occurence of more severe (grade 2 and 3) side effects and assess the tolerance of doxycyline in the prolonged administration.

The observation in the study is biweekly and is continued up to 8 weeks.

Inclusion Criteria:

• diagnosis of metastatic colorectal cancer,
• previously qualified to either cetuximab or panitumumab,
• written consent.

Exclusion Criteria:

• previous administration of cetuximab or panitumumab,
• contradictions to receive oral doxycycline.

Patients with metastatic colorectal cancer, qualified to either cetuximab or panitumumab based systemic treatment (either monotherapy or with chemotherapy) receiving a 100 mg of doxycycline daily.