Despite an increasing interest in oligometastases, the definition of the term “oligometastases” can be very confusing because it has been dependent on the particular research. Many researchers have defined oligometastases as metastases that are limited in both number (typically, less than 5) and location. Another confusing issue is outcome evaluation; researchers have evaluated the outcome of oligometastases by overall survival or local control. […] Hellman and Weichselbaum originally proposed the state of oligometastases in 1995 based on a consideration of the multistep nature of cancer progression. They proposed the existence of an oligometastatic state that was an “intermediate between purely localized lesions and those widely metastatic”. The state was expounded to be “amenable to a curative therapeutic strategy” and “amenable to localized therapy”.
Source: wiktionary