As safety information pertaining to the long-term use of HU remains incomplete in spite of the first safety study (ESCORT-HU), an extension of the latter is proposed. ESCORT-HU Extension study aims at evaluating the long-term safety of Siklos® focusing on some questions regarding its safety when used in current practice in adults and paediatric patients treated with Siklos® and followed for up to 5 years. The study will focus on the following concerns : occurrence and incidence of malignancies, leg ulcers, male fertility impairment and serious unexpected AEs causally related to Siklos®.

Inclusion Criteria:

• Male or female patients with symptomatic SCD,
• ≥ 2 years old,
• Treated with Siklos®,
• Having been informed of the study by the investigator and consenting to participate, or whose parents or legal guardians are consenting for their child to participate.

To allow risk evaluation, participants must belong at least to one of the subpopulations defined below:

• Participants previously enrolled in ESCORT-HU who agree to participate in ESCORT-HU Extension study,

• New participants with any of the following criteria:

  • history of HU treatment for more than 5 years or
  • prepubescent over 10 years of age for girls and 13 years of age for boys at enrolment, or
  • with history of leg ulcer, or
  • pregnant women without interruption of Siklos® 3 months before the beginning of the pregnancy or,
  • males treated with Siklos® whose partner is pregnant and without discontinuation of Siklos® 3 months before the beginning of the pregnancy.

Investigators will be recruited among physicians experienced in SCD management who are the only ones authorised to initiate Siklos® treatment hence to enrol and to follow up the participants. Investigators who are already participating in ESCORT-HU study will be asked to participate in the extension study.

Patient selection will be based on a systematic sampling technique: during the recruitment period, patients fulfilling the inclusion criteria will be informed by their initiating physician about the ESCORT-HU Extension study and enrolled in case they agree to participate.