In order to get further opportunities in the professional field, Chen Saijuan was sent to the Institute of Hematology of St. Louis Hospital, a famous hematology research center in Paris. Prior to this, Zhu Chen was strongly recommended by Professor Kuang Ankun, the famous founder of endocrinology in China, and was sent by the school as a foreign resident in June1984+1October. After arriving in France, Zhu Chen made up his mind to master the basic theories and methods of molecular biology, reveal the pathogenesis of tumors, and create corresponding therapeutic mechanisms. Through investigation, Chen Saijuan realized that cytogenetics and molecular genetics are the important basis of leukemia diagnosis and the breakthrough of leukemia molecular mechanism research, but there is still a lack in the field of hematology in China. Therefore, Chen Saijuan is determined to build a bridge between clinical and molecular research in hematology and explore the pathogenesis of leukemia. In order to concentrate on his research, Chen Saijuan left his son under two years old at home and applied for a doctorate from University of Paris VII, where he studied under the internationally renowned cytogeneticist Laurent Berger. Since then, the basic and clinical research of leukemia has become the career pursued by Chen Saijuan all his life.

At the beginning of his doctoral degree, Chen Saijuan studied the methods of cytogenetic karyotype analysis, and studied the immunophenotype of Philadelphia chromosome (caused by reciprocal translocation of chromosome 9 and chromosome 22) leukemia cells, that is, karyotype analysis and immunophenotype analysis were carried out at the same time without rupturing the cell membrane. At that time, in situ hybridization of chromosome fluorescein was not introduced. Although it took half a year to study, the progress was still not smooth. From 65438 to 0986, molecular biology was in a stage of rapid development. By using Southern and Northern analysis, DNA sequencing, molecular cloning and chromosome walking, Chen Saijuan finally found a new molecular aberration in Philadelphia chromosome-positive acute leukemia. In this aberration, the breaking point of BCR gene on chromosome 22 in Philadelphia is not located in the classical region of chronic myeloid leukemia (intron 12 to 14), but in the first intron of BCR gene, which provides a useful molecular marker for the diagnosis and differential diagnosis of diseases and a working model for the possible mechanism of chromosome translocation in this type of leukemia. During more than three years in France, Chen Saijuan worked nonstop every day 12- 14 hours. Hard work finally brought sweet harvest. Chen Saijuan published 12 papers, among which the first author published 6 papers in Blood, Oncogenes, Nucleic Acid Research and Leukemia. From 65438 to 0989, Chen Saijuan passed the thesis defense with the highest score and obtained the Doctor of Science degree of Paris VII. A French expert who participated in the doctoral thesis defense Committee said: "I have done similar research and know that it is not easy to overcome this problem and it takes a lot of efforts." Chen Saijuan's tutor jokingly said to people, "I can't call her Madame Curie directly, but she is a very resilient woman."

Studying and living in Paris, France for more than three years is the process of Chen Saijuan's scientific research career gradually maturing, which also makes her know the western world for the first time, make many French friends and enter the academic circle. However, inadvertently, a question came quietly: Do you want to stay in France to do handy scientific research and live a comfortable life in Europe, or do you want to go back to China to start a hard business? There are more opportunities for development in western countries if well-meaning friends make suggestions. Chen Saijuan and Zhu Chen had some discussions, but their conclusion was the opposite: China needs more scientific talents. Their love for French culture will never be less, but they love their motherland even more. In fact, Mr. and Mrs. Chen Saijuan kept their children at home all the time when they went abroad. That is to say, they should make up their mind to go back to China and start a business by missing their children.

On July 4th, 1989, Chen Saijuan and Zhu Chen boarded the flight home together. Before leaving, many French colleagues were very worried and persuaded Chen Saijuan and his wife to change their minds. Some senior experts said: don't go back, stay here, you will definitely get tenure and have a very good future. Many people in China don't understand the return of Chen Saijuan and his wife. At that time, "going abroad" was in full swing, and some people even thought that they must have been unable to get along abroad before returning home. Chen Saijuan thought, no matter what people say, let history prove that they have chosen the right path! As for scientific research conditions, we can create them without them. Mr. and Mrs. Chen Saijuan can't talk big, but they can't go against an old saying of China: A drop of water has the grace of a spring. The motherland has nurtured Chen Saijuan, and Chen Saijuan should serve the motherland, especially when the motherland is in trouble. When the French tutor Berger learned that Chen Saijuan and his wife insisted on returning to China to devote themselves to the country's scientific cause, he was also very moved. He personally took Mr. and Mrs. Chen Saijuan to the French Cancer Foundation, and persuaded the person in charge to get the fund of10,000 francs to help Mr. and Mrs. Chen Saijuan return to China to set up a laboratory. At that time,100000 francs was a large sum of money, and Chen Saijuan and his wife bought instruments and equipment and shipped them back to China.