In 1955, cancer cells in the blood were found by Engell HC in Copenhagen.

• Engell HC. Cancer cells in the circulating blood; a clinical study on the occurrence of cancer cells in the peripheral blood and in venous blood draining the tumour area at operation. Acta Chir Scand Suppl. 1955; 201: 1-70.
  
• Sandberg AA, Moore GE.Examination of blood for tumor cells. J Natl Cancer Inst. 1957;19:1-11.

Hiroharu Uno discovered cancer cells in the blood for the first time in Japan and reported it in 1958 (Saishin Igaku 13; 183-191).



Their common point is the pursuit of originality and priority.