• Efficacy of 0.1% topical sirolimus in cutaneous microcystic lymphatic malformation versus topical vehicle [ Time Frame: Day 1, Week 6, Week 20, Month 12 ]
  PGA (Physician Global Assessment) score assessed by the investigator physician (blinded from the treatment). PGA score ranges from 0 (clear) to 5 (severe lesions), and is commonly used in several dermatologic conditions. For each patient, PGA of the area treated with the intervention (0.1% topical sirolimus) will be compared to PGA of the area treated with topical vehicle (inactive comparator)
• Efficacy of 0.1% topical sirolimus vs vehicle regarding each of the following complications of the CMLM: oozing, bleeding, erythema, and thickness [ Time Frame: Day 1, Week 12, Week 20, Month 12 ]
  Assessment by the investigator blinded to treatment with a visual analog scale (VAS) from 0 to 10 (0: no improvement, 10: recovery)
• Number of independent experts who correctly identify which area among both received the active treatment for each patient on the basis of standardised photographs [ Time Frame: Day1, Week 12 ]
  Standardized photographs will be performed at baseline and week 12: the experts will have to identify, at the end of the study, which area among both received the active treatment. In case of disagreement, a consensus will be reached between both experts; if consensus is not reached, a third expert will be sought for final decision. Interpretation by dermatologic experts (i.e correct identification of intervention/vehicle treated area) will be considered as correct or false, and the proportion of correct interpretation will be estimated. The proportion of correct interpretation will be compared to the theoretical 50% value, corresponding to a random assessment. Five photographs will be taken: 1) one of the patient including the malformation 2) one of the malformation (distance of 50 cm), 3) one of the malformation (distance of 15 cm), 4) profile photography and finally 5) three quarter view.
• Global self-reported efficacy of topical sirolimus vs vehicle (with help of parents in case of children under 16 years) [ Time Frame: Week 12, Week 20, Month 12 ]
  Self-assessment of the global improvement of CMLM in both areas using a VAS (Visual Analog Scale) from 0 to 10 (0 no improvement and 10 recovery)
• Functional and esthetic impairments (self-reported with help of parents in case of children under 16 years) [ Time Frame: Day1, Week 20, Month 12 ]
  Using a VAS (Visual Analog Scale) from 0 to 10 (0 no improvement and 10 recovery)
• Pain linked to the CMLM (with help of parents in case of children under 16 years) [ Time Frame: Day1, Week 20, Month 12 ]
  Using a VAS (Visual Analog Scale) from 0 to 10 (0 no pain and 10 worst imaginable pain)
• Effect on quality of life [ Time Frame: Day 1, Week 20, Month 12 ]
  Self-assessment of quality of life using the validated DLQI (Dermatology Life Quality Index) scale, or Child-DLQI for children (equal ou under 16 years old) from 0 to 30 (0 no impact on quality of life and 30 maximum impact on quality of life)
• Evaluation of systemic passage of sirolimus by dosage of serum level of sirolimus [ Time Frame: Week 6, Week 12, Week 20, +/- Week 16 (if CMLM ≥ 30*30 cm and/or ≥900 cm2) ]
  Dosage of serum level of sirolimus
• Number of patients with biological adverse events and total number of biological adverse events (to assess the biological tolerance of topical sirolimus) [ Time Frame: Baseline, Week 12, Week 20 ]
  Number of patients with biological adverse events and total number of biological adverse events (blood samples at baseline, week 12 and week 20)
• Number of patients with clinical adverse events and total number of clinical adverse events (to assess the clinical tolerance of topical sirolimus) [ Time Frame: Week 6, Week 12, Week 20 ]
  Number of patients with clinical adverse events and total number of clinical adverse events (record of local and general adverse events)

This blinded multicentre split body randomized controlled phase 2 trial aims to include 50 patients ≥ 6 years old who have a primary CMLM without an underlying malformation.

The CMLM will be divided into 2 equal areas of the same severity that will be randomly allocated to 0.1% topical sirolimus or topical vehicle for 12 weeks. During the double-blind 12-week period, both topical products will be applied by a nurse to avoid inter-group contamination and for better compliance.

At the end of the 12-week period, the patient/parent will treat the whole area of CMLM with 0.1% topical sirolimus on remaining lesions, for 8 more weeks. Patients will also be seen at week 20 (treatment will be stopped) and at month 12 to evaluate long-term efficacy.

• Vascular Malformations
• Lymphatic Malformation

• Drug: Topical 0.1% Sirolimus
  The formulation is 0.03 g rapamycin, 1.5 g Transcutol, Quantum Satis (QS) 30g Excipial® hydrocream, corresponding to a concentration at 0.1%. The cream will be packaged in 30 ml aluminium tubes.
  Other Name: Verum
• Drug: Topical Vehicle
  The same vehicle than the one used in the topical 0.1% sirolimus preparation will be used for the other half area of CMLM, i.e. Excipial® hydrocream. It will be packaged to maintain the double blind way of this trial and will be undistinguishable from the sirolimus cream.
  Other Name: Placebo

• Experimental: Topical sirolimus
  The experimental group will consist in one area of the CMLM (almost half of it) that will receive 0.1% sirolimus preparation. This product will be applied 1/day on the randomly allocated area, by a nurse at home, during 12 weeks.
  Intervention: Drug: Topical 0.1% Sirolimus
• Placebo Comparator: Vehicle
  The control group will consist in the other half area of the CMLM, that will receive the same vehicle than the one used in the topical 0.1% sirolimus preparation. It will be applied 1/day in the corresponding area by a nurse, at home, during 12 weeks.
  Intervention: Drug: Topical Vehicle

Inclusion Criteria:

• Patients ≥ 6 years
• Updated immunization schedule
• Diagnosis of primary cutaneous microcystic lymphatic malformation (CMLM) confirmed by histopathological or dermoscopic examination, with or without an underlying malformation or a syndromic malformation (Protée syndrome for instance), responsible for impairment (oozing, bleeding and/or pain)
• CMLM ≥ 20 cm2, that can be divided into 2 parts of similar severity
• Informed, written consent of the subject and his/her parents if < 18 years
• Rights to French social security (including CMU)

Exclusion Criteria:

• Patients with lymphatic malformation requiring a continued background therapy (involving deep organs)
• Secondary lymphatic malformations (lymphangiectasia post-radiotherapy, etc)
• Previous treatment with oral or topical mTOR inhibitors within 12 months before inclusion
• Previous treatment with oral or topical steroids within 10 days before inclusion
• Immunosuppression (immunosuppressive disease or immunosuppressive treatment)
• Ongoing neoplasia
• Active chronic infectious disease (Hepatitis B Virus, Hepatitis C Virus, Human Immunodeficiency Virus, etc)
• Local fungal, viral (Herpes Simplex Virus, Varicella Zoster Virus, etc) or bacterial infection on the site of the CMLM (based on clinical examination)
• Skin necrosis
• Known allergy to one of the components of the topical sirolimus preparation or vehicle
• Women of child-bearing potential (including teenagers) not using a reliable contraceptive method until the end of the study
• Pregnant or breastfeeding women
• Subject already involved in another therapeutic trial