Squamous Cell Carcinoma Antigen (SCCA) contributes to the pathogenesis of psoriasis by inhibiting cell apoptosis, exacerbating epidermal hyperplasia and skin inflammation. Three studies have shown a correlation between blood levels of SCCA and the severity of psoriasis.

Clinical scores of psoriasis severity are used in consultation to guide treatment of the disease (initiation of systemic therapy, dose escalation) but they suffer from several pitfalls: lack of inter- and intra-observer reproducibility, consumption of medical time.

A readily available, inexpensive (24 euros) blood marker could be an interesting alternative to these clinical scores.

Squamous Cell Carcinoma Antigen (SCCA) contributes to the pathogenesis of psoriasis by inhibiting cell apoptosis, exacerbating epidermal hyperplasia and skin inflammation. Three studies have shown a correlation between blood levels of SCCA and the severity of psoriasis.

Clinical scores of psoriasis severity are used in consultation to guide treatment of the disease (initiation of systemic therapy, dose escalation). The PASI (Psoriasis Assessment Severity Index, minimum score 0, maximum 72) is the most widely used. It suffers from several pitfalls: lack of inter- and intra-observer reproducibility, consumption of medical time. This PASI score was "unavoidable" in the international clinical studies used to obtain marketing authorisation for medicines. The PGA (Physician global assessment) is simpler and less time-consuming, ranging from 0 to 4, but is not very discriminating. More recently, a "Simplified Psoriasis Index" (proSPI) health professional score has been developed, which correlates well with PASI for the severity component of psoriasis and with quality of life for the psychological component of the disease. It is less time-consuming to establish than PASI, but suffers like all clinical scores from a problem of inter- and intra-observer reproducibility.

A readily available, inexpensive (24 euros) blood marker could be an interesting alternative to these clinical scores.

Inclusion Criteria:

• Age ≥ 18 years old
• Patient with skin psoriasis (new and untreated or being treated, flare-up or stable, possibly bleached)
• Requiring a blood sample for disease or treatment monitoring

Exclusion Criteria:

• History of invasive mucosal squamous cell carcinoma, or squamous cell carcinoma of the skin with lymph node or visceral recurrence.
• Patient under guardianship or curatorship
• Opposition to participation in the study

Patients with psoriasis