A Novel Aromatase Inhibitor, Leflutrozole, for Treatment of Non-Obstructive Azoospermia

Inclusion Criteria: * Signed informed consent by participant * Signed informed consent by participant's partner (must just be obtained before the par-ticipant starts treatment at Visit 1), if applicable, regarding blood samples, data collec-tion about fertility treatment as well as pregnancy and pregnancy outcome * 18-55 years * Azoospermia verified by at least 2 semen samples, average semen volume \>= 1,0 ml with no identifiable sign of obstruction (samples taken at Visit -1 and at Visit 0 prior to confirmation of eligibility and dosing). * Serum AMH or Inhibin B level above the lower limit of quantification (LLOQ) at screening or within 6 months prior to screening * Testosterone \< 15 nmol/L at screening or within 6 months prior to screening * Serum estradiol above the lower limit of normal range (48 pmol/L) at screening or within 6 months prior to screening Exclusion Criteria: * Klinefelter or other major genetic conditions including large deletions on sex chromosomes * Average testis size \> 20 mL unless obstruction has been excluded * TESE procedure \< ½ year ago * LH concentration \> 15 IU/L at screening * Current abuse of steroids * BMI \> 45 kg/m2 * Severe chronic diseases requiring daily medication * Prior thromboembolic event within the last 24 months * Cardiovascular event within the last 6 months judged as significant by the investigator * Osteoporosis requiring medical treatment * Use of any prescription or non-prescription medication (apart from routine vitamins, occasional use of paracetamol, acetylsalicylic acid, or ibuprofen) which could interfere with pharmacokinetic or pharmacodynamic results, as judged by the investigator, such as: * Herbal products and non-routine vitamins * Insulin * Medication such as systemic corticosteroids, tricyclic antidepressants, and atypical antipsychotics * Surgery scheduled for the trial duration period, except for minor, non-gastrointestinal surgical procedures at the discretion of the investigator * Cancer (past or present, except basal cell skin cancer or squamous cell skin cancer), which in the investigator's opinion could interfere with the results of the trial * Serum prostate specific antigen (PSA) \> 3 ng/mL at screening or within 6 months prior to screening * Hematocrit \>50% at screening or within 6 months prior to screening * Mental incapacity, language barriers or unwillingness to comply with the requirements of the protocol, which may preclude adequate understanding or co-operation during the trial, as judged by the investigator