After completing his postgraduate internship, Dr. Daniel Maliszewski began his residency in general surgery at the Department of Surgical Oncology of the University Clinical Center in Gdańsk. In 2016, he became a board-certified general surgeon and was awarded a PhD in Medical Sciences for his dissertation entitled "Comparison of Biomarker Expression in Primary Breast Tumors and Local Recurrence in Breast Cancer Patients." He is currently completing his specialization in surgical oncology. In the same year, he passed the prestigious European Board of Surgery Qualification (EBSQ) in Breast Surgery examination.
He also completed postgraduate studies in Healthcare Finance and Management at the Gdańsk School of Management. He currently works in the Departments of General and Oncological Surgery at the J. Korczak Provincial Specialist Hospital in Słupsk and the Specialist Hospital in Kościerzyna, while continuing his specialist training in surgical oncology.
His clinical practice focuses on breast oncological and reconstructive surgery, abdominal wall surgery, and oncoplastic facial surgery. His particular area of interest is reconstructive surgery using flap and microsurgical techniques. He is one of the few surgeons in Poland specializing in the surgical treatment of lymphedema. As part of his clinical and scientific work, he collaborates closely with leading international centers, including the Department of Plastic Surgery at Sana Krankenhaus Gerresheim in Düsseldorf and the Department of Gynecology at Helios Klinikum Bad Saarow.
He has completed 25 international clinical fellowships and 30 international hands-on surgical courses. He is one of only three Polish surgeons to hold the European Board of Surgery Qualification (EBSQ) in Breast Surgery certification. In 2017, he received the Hipokrates "Doctor of the Year" award presented by Głos Pomorza. Each month, he performs approximately 30–45 breast and reconstructive surgical procedures under general anesthesia.