Abstract Background Chronic myeloid leukaemia BCR-ABL1 + (CML) is a clonal disorder of a pluripotent stem cell. The disease accounts for around 15% of leukaemias and may occur at any age. The diagnosis of CML is rarely difficult and is assisted by the characteristic presence of the Philadelphia (Ph) chromosome. This results from the t (9;22) (q34; q11) translocation between chromosomes 9 and 22, as a result of which part of the oncogene ABL1 is moved to the BCR gene on chromosome 22. and part of chromosome 22 moves to chromosome 9. The abnormal chromosome 22 is the Ph chromosome. Aim of the Work To measure the level of PTCH1 in newly diagnosed CP-CML and to find correlation between the level of PTCH1in those patients and response to first line of treatment; imatinib and other prognostic factors Patients and Methods In our study there are 50 patients newly diagnosed cml recruited from hematology out patients clinic in ain shams university within duration august 2021 –april 2022.We have measured level of PTCH1 protein in newly diagnosed CP-CML and its follow up after 6months Results the studies show that 25% of patients discontinue imatinib due to lack of efficacy. A few years ago, two second-generation tyrosine kinase inhibitors (TKIs), Dasatinib and Nilotinib, were approved for first-line treatment, increasing the options available for patients diagnosed with CP- CML.Currently, the best way to adjust treatment to fit the severity of the disease is by assessing the response at different milestones. One milestone is the BCR-ABL1/ABL1 transcript level at 3 months; a level >10% 3 months after starting treatment has been related to a worse subsequent imatinib response. However, whether a change in therapy is warranted based on this single determination is controversial. Conclusion Patched homolog 1 gene (PTCH1) is marker for predicting first line of treatment imatinib response in chronic myeloid leukemia patients in chronic phase in correlation with response to imatinib. It is detected by PCR and proved to be a reliable marker to detect early imatinib response in chronic myeloid leukemia patients in chronic phase. In our study, we measured level of (PTCH1) in chronic myeloid leukemia patients in chronic phase using ELISA as a cost benefit in comparison to PCR in newly diagnosed cml patients on first line of treatment imatinib then follow up after 6 months. We found that it is a reliable marker, sensitive and specific to detect imatinib response.