1. Katanoda K, Matsuda T, Matsuda A, et al. An updated report of the trends in cancer incidence and mortality in Japan. Jpn J Clin Oncol. 2013;43:492–507.
2. Primrose JN, Fox RP, Palmer DH, et al. Capecitabine compared with observation in resected biliary tract cancer (BILCAP): a randomised, controlled, multicentre, phase 3 study. Lancet Oncol. 2019;20:663–73.
3. Sulpice L, Rayar M, Boucher E, et al. Treatment of recurrent intrahepatic cholangiocarcinoma. Br J Surg. 2012;99:1711–7.
4. Takahashi Y, Ebata T, Yokoyama Y, et al. Surgery for recurrent biliary tract cancer: a single-center experience with 74 consecu- tive resections. Ann Surg. 2015;262:121–9.
5. Miyazaki Y, Kokudo T, Amikura K, et al. Survival of surgery for recurrent biliary tract cancer: a single-center experience and systematic review of literature. Jpn J Clin Oncol. 2017;47:206–12.
6. Park HM, Yun SP, Lee EC, et al. Outcomes for patients with recurrent intrahepatic cholangiocarcinoma after surgery. Ann Surg Oncol. 2016;23(13):4392–400.
7. Yoh T, Hatano E, Seo S, et al. Long-term survival of recurrent intrahepatic cholangiocarcinoma: the impact and selection of repeat surgery. World J Surg. 2018;42:1848–56.
8. Kim E, Kim YJ, Kim K, et al. Salvage radiotherapy for locore- gionally recurrent extrahepatic bile duct cancer after radical surgery. Br J Radiol. 2017;90:20170308.
9. Kim SW, Lim DH, Park HC, et al. Salvage radiation therapy for isolated local recurrence of extrahepatic cholangiocarcinoma after radical surgery: a retrospective study. Ann Surg Oncol. 2015;22:1308–14.
10. Ercolani G, Vetrone G, Grazi GL, et al. Intrahepatic cholangio- carcinoma: primary liver resection and aggressive multimodal treatment of recurrence significantly prolong survival. Ann Surg. 2010;252:107–14.
11. Zhang SJ, Hu P, Wang N, et al. Thermal ablation versus repeated hepatic resection for recurrent intrahepatic cholangiocarcinoma. Ann Surg Oncol 2013;20(11):3596–602.
12. Park SY, Kim JH, Won HJ, et al. Radiofrequency ablation of hepatic metastases after curative resection of extrahepatic cholangiocarcinoma. AJR Am J Roentgenol. 2011;197:W1129–34.
13. Spolverato G, Kim Y, Alexandrescu S, et al. Management and outcomes of patients with recurrent intrahepatic K. Morino et al. cholangiocarcinoma following previous curative-intent surgical resection. Ann Surg Oncol. 2016;23:235–43.
14. Miyazaki M, Shimizu H, Yoshitomi H, et al. Clinical implication of surgical resection for recurrent biliary tract cancer: does it work or not? Ann Gastroenterol Surg. 2017;1:164–70.
15. Keane FK, Zhu AX, Hong TS. Radiotherapy for biliary tract cancers. Semin Radiat Oncol. 2018;28:342–50.
16. Hellman S, Weichselbaum RR. Oligometastases. J Clin Oncol. 1995;13:8–10.
17. Niibe Y, Hayakawa K. Oligometastases and oligo-recurrence: the new era of cancer therapy. Jpn J Clin Oncol. 2010;40:107–11.
18. Tait CR, Waterworth A, Loncaster J, et al. The oligometastatic state in breast cancer: hypothesis or reality. Breast. 2005;14:87–93.
19. Dethy S, Piccart MJ, Paesmans M, et al. History of brain and epidural metastases from breast cancer in relation with the dis- ease evolution outside the central nervous system. Eur Neurol. 1995;35:38–42.
20. Oh Y, Taylor S, Bekele BN, et al. Number of metastatic sites is a strong predictor of survival in patients with nonsmall cell lung cancer with or without brain metastases. Cancer. 2009;115:2930–38.
21. Foster CC, Weichselbaum RR, Pitroda SP. Oligometastatic prostate cancer: reality or figment of imagination? Cancer. 2019;125:340–52.
22. Ost P, Reynders D, Decaestecker K, et al. Surveillance or metastasis-directed therapy for oligometastatic prostate cancer recurrence: a prospective, randomized, multicenter phase II trial. J Clin Oncol. 2018;36:446–53.
23. Jingu K, Matsushita H, Yamamoto T, et al. Stereotactic radio- therapy for pulmonary oligometastases from colorectal cancer: a systematic review and meta-analysis. Technol Cancer Res Treat. 2018;17:1533033818794936.
24. Chiapponi C, Berlth F, Plum PS, et al. Oligometastatic disease in upper gastrointestinal cancer—how to proceed? Visc Med. 2017;33:31–4.
25. Hellman S. Karnofsky memorial lecture. Natural history of small breast cancers. J Clin Oncol. 1994;12:2229–34.
26. Valle J, Wasan H, Palmer DH, et al. Cisplatin plus gemcitabine versus gemcitabine for biliary tract cancer. N Engl J Med. 2010;362:1273–81.
27. Okusaka T, Nakachi K, Fukutomi A, et al. Gemcitabine alone or in combination with cisplatin in patients with biliary tract cancer: a comparative multicentre study in Japan. Br J Cancer. 2010;103:469–74.
28. Sobin LH, Gospodarowicz MK, Wittekind C, editors. TNM classification of malignant tumors, 7th ed. New York: Wiley; 2009.
29. Brookhart MA, Schneeweiss S, Rothman KJ, et al. Variable selection for propensity score models. Am J Epidemiol. 2006;163:1149–56.
30. Stenestrand U, Wallentin L. Early revascularisation and 1-year survival in 14-day survivors of acute myocardial infarction: a prospective cohort study. Lancet. 2002;359:1805–11.
31. Austin PC. An introduction to propensity score methods for reducing the effects of confounding in observational studies. Multivariate Behav Res. 2011;46:399–424.
32. Zhang XF, Beal EW, Chakedis J, et al. Defining early recurrence of hilar cholangiocarcinoma after curative-intent surgery: a multi- institutional study from the US extrahepatic biliary malignancy consortium. World J Surg. 2018;42:2919–29.
33. Ercolani G, Dazzi A, Giovinazzo F, et al. Intrahepatic, peri-hilar and distal cholangiocarcinoma: three different locations of the same tumor or three different tumors? Eur J Surg Oncol. 2015;41:1162–9.