Graduated from the Faculty of Medicine of the University of Tartu and specialised as an oncologist and general surgeon. Participated in training courses and conferences in oncology, general surgery, plastic surgery and dermatoscopy in Finland, Sweden, Norway, Denmark, the Netherlands, Belgium, Germany, Switzerland, Austria, Italy, England, France, Russia, Israel and the United States.

Participated in several international research projects, published articles, presented papers at international congresses and lectured at continuing medical education courses.

Dr Niin is a member of the Estonian Association of Surgeons, the Estonian Society of Oncologists, the European Organisation for Research and Treatment of Cancer (EORTC) melanoma working group and the International Dermatoscopy Society (IDS); since 2010. Estonia’s representative in the Global Melanoma Task Force (GMTF) since 2006. Dr Niin is also a member of the Estonian Society of Plastic and Reconstructive Surgeons and a member of the International Plastic Reconstructive and Aesthetic Surgery Association (IPRAS).