Rationale and Objectives
An ever-expanding body of biological, genetic, and clinical evidence has brought to light the presence of the oligometastatic state of cancer, which is considered between localized disease and widespread metastases. Indeed, in some patients with oligometastatic disease, curative therapy is possible.
Conclusions
For select cancer histologies, aggressive focal therapy of oligometastatic lesions is already the clinical standard of care (i.e. colorectal cancer and sarcomas), while for other tumor types the evidence is still emerging (i.e. prostate, breast, etc.). It is increasingly important, therefore, for the radiologist interpreting oncology patients’ staging or restaging examinations to be aware of those diseases for which targeted therapy of oligometastases may be undertaken to effectively guide such management. The improved imaging resolution provided by technological advances promise to aid in the detection of subtle sites of disease to ensure the identification of patients with oligometastases amenable to targeted treatment.
Introduction
In a landmark paper in 1995, Hellman and Weichselbaum postulated the oligometastatic state of oncologic disease, in which patients may harbor a limited number of metastatic lesions. This state was viewed as existing on a continuum between localized and diffuse metastatic diseases, with oligometastic patients potentially receiving improved systemic control or even cure of their disease from treatment directed at these discrete metastatic foci. Indeed, there is increasing evidence on the molecular and genetic levels that oligometastatic disease is a distinct entity from diffusely metastatic disease, with the metastatic cells in oligometastases displaying a phenotype that lacks some of the elements necessary to bring about widespread metastases . This recognition results in a profoundly important change from the dogma that a small number of identifiable metastatic lesions necessarily connote widespread systemic disease and a stage of cancer only amenable to systemic chemotherapy.
In light of this shifting perception about the nature of metastatic cancer, for those patients in whom there are a small number of discretely identifiable lesions, it is becoming increasingly incumbent upon the interpreting radiologist to delineate each of those lesions. An approach in which only an index lesion is specifically commented upon when a small number of other lesions are present may be inadequate in certain clinical contexts. Indeed, the radiologist should be cognizant of the need to guide treatment in cases of oligometastatic disease, which can include a variety of local therapies such as radiation, surgery, or cryotherapy. Although a number of definitions of oligometastatic disease have been suggested, and refinement of the concept of oligometastasis may eventually arrive at different definitions for different diseases, most commonly five or fewer distinct lesions are considered oligometastases .
This opinion piece discusses the malignancies in which aggressive treatment of oligometastic disease is already widely clinically accepted, as well as those in which there is emerging evidence that such treatment may be beneficial. We also refer the reader to an excellent and comprehensive review by Reyes and Pienta that discusses the biology of oligometastsic disease and the current clinical trials ongoing within this realm.
Colorectal Cancer
Oligometastatic colorectal cancer involving the liver represents a prototype for the aggressive treatment of a small number of metastatic lesions, with liver resection taking place before, after, or at the time of resection of the primary . Thermal and radiofrequency ablation can also be used in the treatment of oligometastatic disease to the liver. Treatment of oligometastatic colorectal cancer to the liver can be curative in some patients . In any case of colorectal cancer staging or restaging with cross-sectional imaging, it is of utmost importance to examine the liver for any suspicious lesion(s) and to accurately identify their locations within the liver, unless such lesions are widespread or diffuse.
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Prostate Cancer
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Renal Cell Carcinoma (RCC)
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Sarcomas
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Lung Cancer
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Other Cancer Types
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Conclusion
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