The goal of this retrospective multicenter observational study is to understand and evaluate the diagnostic and therapeutic management of pure forms of Florid Lobular Carcinoma In Situ (FLCIS) and Pleomorphic Lobular Carcinoma In Situ (PLCIS) of the breast. It addresses the significant challenges and controversies surrounding their clinical management, due to a lack of consensus or approved international guidelines. The main questions this study aims to answer are: * How is the diagnostic process for pure FLCIS and PLCIS currently managed? * What are the primary therapeutic approaches for these specific breast conditions? * How are positive and close surgical excision margins handled? * Is adjuvant treatment, such as hormone therapy and radiotherapy, necessary? * What factors are associated with recurrences? * What are the rates of recurrences and/or upgrade to invasive carcinoma? Participants will retrospectively collect all cases of pure FLCIS and PLCIS, reporting detailed data about their diagnostic and therapeutic management, as well as clinical and survival outcomes. Methodology: This international multicenter retrospective study will collect cases involving the pure forms of FLCIS and PLCIS of the breast. The study aims to provide insights into the current diagnostic and therapeutic approaches, along with the identification of opportunities to enhance clinical management, ultimately providing evidence-based recommendations and addressing the current lack of scientific literature regarding their treatment.