We aim to implement our vast knowledge about B cell immune responses in mice for understanding the function of tumor infiltrating B cells in human cancer. Ovarian and pancreatic cancers rank among the five deadliest types of cancers. Their lack of effective screening strategies and their poor prognoses constitutes an urgent need for the discovery of novel means for early detection and therapy. Immunotherapeutic approaches in oncology underscores the pivotal role of the immune system in the treatment of cancer. Anti-tumor antibodies are one of the safest and efficient therapies available for treatment of cancer patients and in the last decade many antibodies were approved for clinical use. These antibodies are limited so far to rare antigens and to small types of cancer. Thus, there is a great need for discovery of new anti-tumor antibodies. The development of therapeutic antibodies requires a deep understanding of the interplay between the immune system and cancer cells. We have developed a screening strategy to detect auto-antibodies in the malignant ascites fluids derived from cancer patients. This strategy was employed in order to generate a potential “target bank” for testing future cloned antibodies.