Recurrence or metastasis of cancer has been considered to occur in the last stage of the patient's life. However, the new notions of oligometastases and oligo-recurrence have been proposed and the paradigm shift in the conceptualization of cancer metastasis or cancer recurrence. Oligometastases is the state in which the patient shows distant relapse in only a limited number of regions. Local therapy such as surgery, radiotherapy and radiofrequency ablation for the relapsed sites could thus improve patient's survival. On the other hand, oligo-recurrence is a notion similar to oligometastases. However, the conditions of oligo-recurrence has a primary site of the cancer controlled, meaning that all gross recurrent or metastatic sites could be treated using local therapy.

Oligometastases and oligo-recurrence are among the most important notions of metastatic and recurrent cancer. The concept of oligometastases is related to the notion that cancer patients with 1–5 metastatic or recurrent lesions that could be treated by local therapy achieve long-term survival or cure, while the concept of oligo-recurrence is related to the notion that cancer patients with 1–5 metastatic or recurrent lesions that could be treated by local therapy have controlled primary lesions. Achievement of long-term survival or cure in patients with oligometastases and oligo-recurrence is cancer and organ specific. These facts rely on the seed and soil theory and multiple steps of cancer progression. Oligo-recurrence is considered to have a better prognosis than oligometastases. In patients with oligometastases and oligo-recurrence, the oligometastases and oligo-recurrence are sometimes cured with only local therapy, which is an example of the abscopal effect, previously described in relation to cure of lesions outside of the field of radiation therapy without systemic therapy. Oligometastases and oligo-recurrence can now be cured by less invasive local treatment methods combined with systemic therapy. The mechanisms of oligometastases and oligo-recurrence, as well as novel insights into these important concepts, are presented in this paper.

Introduction: The abscopal effect is the effect of radiation therapy at a site distant to the area of irradiation. This is not a common event and has not been clearly defined, resulting in few reported cases in the literature. We discuss this phenomenon in a patient with hepatocellular carcinoma. Case presentation: A 63-year-old Japanese man underwent extended right hepatic lobectomy for hepatocellular carcinoma. During his follow-up examination, a single lung metastasis and a single mediastinal lymph node metastasis were found. Trans-catheter arterial embolization was initially attempted to treat the mediastinal tumor, however this approach failed to take effect and carried risks of spinal artery embolism. External-beam irradiation, with a dose of 2.25 Gy per fraction, was performed using an antero-posterior parallel-opposed technique (total dose, 60.75 Gy). A computed tomography scan performed one month after starting radiotherapy showed a remarkable reduction of the mediastinal lymph node metastasis. In addition to this, we observed spontaneous shrinking of the lung metastasis, which was located in the right lower lobe and out of the radiation field. No chemotherapy was given during the period. There has been no recurrence of either the lung metastasis or the mediastinal lymph node metastasis during a follow-up 10 years after the radiotherapy. Conclusion: We observed a rare abscopal effect in a site distant from the area of irradiation. Irradiation of the mediastinum resulted in tumor mass regression in the untreated lung tumor.

Background To investigate the prognostic value of oligo-recurrence in patients with brain-only oligometastases of non-small cell lung cancer (NSCLC) treated with stereotactic radiosurgery (SRS) or stereotactic radiotherapy (SRT). Methods Patients treated with SRS or SRT for brain-only NSCLC oligometastases in 6 high-volume institutions in Japan between 1996 and 2008 were reviewed. Eligible patients met 1), 2), and 4) or 1), 3), and 4) of the following: 1) NSCLC with 1 to 4 brain metastases on magnetic resonance imaging (MRI) treated with SRS or SRT; 2) control of the primary lesions (thorax) at the time of SRS or SRT for brain metastases (patients meeting this criterion formed the oligo-recurrence group); 3) with SRS or SRT for brain metastases, concomitant treatment for active primary lesions (thorax) with curative surgery or curative stereotactic body radiotherapy (SBRT), or curative chemoradiotherapy (sync-oligometastases group); and 4) Karnofsky performance status (KPS) ≥70. Results The median overall survival (OS) of all 61 patients was 26 months (95 % CI: 17.5–34.5 months). The 2-year and 5-year overall survival rates were 60.7 and 15.7 %, respectively. Stratified by oligostatus, the sync-oligometastases group achieved a median OS of 18 months (95 % CI: 14.8–21.1 months) and a 5-year OS of 0 %, while the oligo-recurrence group achieved a median OS of 41 months (95 % CI: 27.8–54.2 months) and a 5-year OS of 18.6 %. On multivariate analysis, oligo-recurrence was the only significant independent factor related to a favorable prognosis (hazard ratio: 0.253 (95 % CI: 0.082–0.043) (p = 0.025). Conclusions The presence of oligo-recurrence can predict a favorable prognosis of brain-only oligometastases in patients with NSCLC treated with SRS or SRT.