Oligoprogression

Oligoprogression is an emerging concept in oncology, denoting a state where after an initially successfully systemic therapy of disseminated metastases, a single/few lesions display further progression. 

Terminology

A key difference between the related concepts of oligometastasis and oligoprogression is that a patient with the latter can have generally any number of metastases as long as only a solitary or a select few show progression, with the rest displaying either regression or stability while the patient continues to receive systemic antitumor therapy ¹. By definition, the state of oligoprogression occurs after initially successful therapy of polymetastatic disease, where disease progression is encountered only in a minority of the affected sites ². 

Pathology

Oligoprogression is caused by the emergence of tumour cell phenotypes of varying aggressivity and thereby of differing progression potential during the clonal evolution of the disseminated tumour.  

Non-small cell lung cancer (NSCLC) is one of the best-studied examples of malignant diseases capable of demonstrating an oligoprogression pattern. Existing evidence also shows that clear cell renal cell carcinoma and prostate cancer also commonly show oligoprogression ¹. Oligoprogression due to selective subclonal drug resistance is increasingly encountered since the advent of targeted, molecular antitumor agents ². 

Treatment and prognosis

Targeted therapies such as stereotactic radiosurgery, cryotherapy and surgery are the mainstays for the treatment of patients showing tumour oligoprogression ¹. Selective, minimally invasive therapy can thereby allow the continuation of the systemic therapy that is otherwise effective against the majority of the tumour cell subclones ².  

Practical points

Knowledge of oligoprogression as a concept is crucial in radiology practice, especially as these patients with multiple metastases among which only a select few show progression during the systemic (chemo-, or biological therapy) may still benefit from its continuation (as it does affect the majority of the metastatic burden), whilst the single or few metastatic foci showing oligoprogression are excellent candidates for other targeted therapies (e.g. surgical resection, ablation, selective chemoembolisation, focused cryo- or radiotherapy)¹. Thus, if only a single, or a small minority of metastatic foci show interval progression, the possibility of an oligoprogressive disease must be considered. The criteria of oligoprogression have not yet solidified, with some studies describing a precise number e.g. four or fewer sites of progression in NSCLC as the prerequisite for it ³. 

It is important to bear in mind that current reporting standards (e.g. RECIST v.1.1) are not yet adapted to the concept of oligoprogression, furthermore, it is currently uncertain which imaging modalities are the most suitable to distinguish oligoprogression from polyprogression ².