The company provides oncology treatment information from 100,000 US patients to pharmaceutical, biotechnology and financial companies.
Aegis said that it would complement Synovate Healthcare's existing oncology portfolio, which includes the Global Oncology Monitor.
Robert Lerwill, chief executive of Aegis, said: "The acquisition of Oncology Inc. underlines our commitment to leadership in a key therapy area. Onocology is a strategic addition to our group, bringing new expertise and capacity to grow Synovate's global lead in oncology."
At the same time, Aegis said it had bought Finnish digital marketing and design agency White Sheep. The agency, which was founded in 2003, will be rebranded Suddenly Helskinki, and become part of Aegis' digital division Isobar. The Suddenly network already has offices in Stockholm, Oslo, Gothenberg and Copenhagen.
Terms of the deals were not disclosed.