Editorial: Increasing importance of patients-generated real world data for healthcare policy decisions about medicinal products: volume III.

Breast cancer is the most common type of cancer in women. According to GLOBOCAN 2022 data, breast cancer ranks second in global cancer incidence, accounting for 11.6% of all cancer cases with an estimated 2.3 million new cases. In the same year, 666 000 deaths occurred due to breast cancer, accounting for 6.9% of global cancer deaths and placing breast cancer fourth in cancer mortality (Bray et al. ). Despite early diagnosis opportunities, advanced treatment methods, and increased survival rates, breast cancer affects an individual's life in multiple ways: physically, psychologically, and socially throughout the diagnosis and treatment process and beyond (Culbertson et al. ). The ratio between the lengths of the second (2D; index finger) and fourth (4D; ring finger) digits, commonly referred to as the 2D:4D ratio, is thought to be established during early prenatal development and to remain relatively stable throughout life (Manning et al. ; Manning ). Experimental studies suggest that this ratio is influenced by the balance between prenatal androgen and estrogen signaling during a critical period of fetal digit development. Androgen receptor (AR) and estrogen receptor alpha (ER‐α) expression are greater in the developing fourth digit than in the second digit. Increased androgen signaling promotes the growth of the fourth digit, resulting in a lower 2D:4D ratio, whereas increased estrogen signaling is associated with relatively reduced growth of the fourth digit and a higher 2D:4D ratio. These hormonal influences act during a narrow developmental window and are thought to produce a lifelong phenotypic marker of prenatal hormonal exposure (Zheng and Cohn ). While a lower 2D:4D ratio is generally observed in men, this ratio tends to be higher in women. This sexual dimorphism is thought to reflect differences in prenatal androgen and estrogen exposure. Because prenatal hormonal conditions may influence the development of multiple organ systems and contribute to disease susceptibility later in life, the 2D:4D ratio has been proposed as an indirect and non‐invasive marker of prenatal hormonal influences that may be relevant to adult health outcomes (Manning et al. ; Manning ; Grotmol et al. ). Reproductive hormones are known to play an important role in the development and progression of breast cancer, a hormone‐dependent malignancy (Folkerd and Dowsett ). In addition, there is growing interest in the possibility that hormonal conditions during prenatal development may contribute to breast cancer susceptibility later in life, although the available evidence remains limited and is still evolving (Grotmol et al. ).