Endometriosis is a chronic gynecological disease characterized by the presence of endometrial-like tissue outside the uterus and is frequently associated with pelvic pain and infertility. Increasing evidence suggests that immune dysfunction may contribute to the development and persistence of the disease.

The purpose of this prospective case-control study is to compare immune cell characteristics in women with deep endometriosis and women without endometriosis during the secretory phase of the menstrual cycle. Participants will undergo collection of clinical data, blood samples, endometrial samples, and vaginal microbiota samples. For participants undergoing clinically indicated pelvic surgery, additional biological samples may be collected during the procedure. The study aims to improve understanding of the immune mechanisms involved in endometriosis and to identify potential biomarkers associated with the disease.

Endometriosis affects approximately 10-15% of women of reproductive age and represents a major public health concern. Despite its high prevalence, the pathophysiological mechanisms underlying the disease remain incompletely understood. Increasing evidence suggests that alterations in the immune environment of the endometrium may contribute to the establishment and progression of endometriosis. In particular, uterine immune cells may play a role in regulating local inflammation and tissue homeostasis. Characterizing these immune mechanisms may improve understanding of disease development and identify potential biomarkers associated with endometriosis.

PAINLESS is a prospective, single-center, pilot case-control study conducted at Foch Hospital (Suresnes, France). The study will enroll 50 adult women, including 25 participants with confirmed deep endometriosis and 25 control participants without endometriosis.

Biological samples will be collected during the secretory phase of the menstrual cycle (days 16-24). Depending on clinical management, study procedures may include:

• Collection of demographic and clinical data
• Assessment of symptoms and quality of life
• Blood sampling
• Endometrial sampling
• Vaginal microbiota sampling
• Collection of additional biological specimens during clinically indicated pelvic surgery.

Biological samples will be analyzed to characterize immune cell populations, evaluate soluble immune mediators, investigate associations with hormonal and clinical parameters, and explore biological mechanisms involved in endometriosis.The primary objective is to compare the expression of immune-related markers in endometrial and peritoneal samples obtained from women with endometriosis and controls. Secondary objectives include characterization of immune cell phenotypes and functions, evaluation of immune-related soluble factors, investigation of interactions between immune and endometrial cells, assessment of correlations with hormonal and clinical data, exploratory genetic analyses, and creation of a vaginal microbiota biobank. Results from this pilot study are expected to provide preliminary data for future research aimed at improving the understanding, diagnosis, and management of endometriosis.

Inclusion Criteria:

• Endometriosis Group
• Female participant aged 18 years or older.
• Confirmed diagnosis of deep endometriosis by imaging or surgery.
• Pelvic pain and/or severe dysmenorrhea (Visual Analog Scale > 4).
• Premenopausal.
• No contraceptive or hormonal treatment during the study menstrual cycle.
• Affiliated with a health insurance system.
• Able and willing to provide written informed consent.
• Control Group
• Female participant aged 18 years or older.
• No diagnosis of endometriosis.
• Premenopausal.
• No contraceptive or hormonal treatment during the study menstrual cycle.
• No chronic pelvic pain or severe dysmenorrhea (Visual Analog Scale < 4).
• Affiliated with a health insurance system.
• Able and willing to provide written informed consent.

Exclusion Criteria:

• Current infection.
• Active cancer.
• Active autoimmune disease.
• Concomitant hormonal treatment.
• Pregnancy.
• Participant under guardianship or legal protection.
• Participant deprived of liberty.

Participants must be individuals who identify as female and meet all study eligibility criteria.