A 63-year-old man presented to our department with exertional dyspnoea. He had a 2-year history of dyspnoea that had worsened over the previous 6 months. He had also been diagnosed with CML at the age of 55, for which a first-generation TKI, imatinib (400 mg daily), was prescribed as his first-line therapy. However, since this caused facial oedema and massive pleural effusion, a second-generation TKI, dasatinib (100 mg daily), was chosen as his second-line therapy 5 years before presentation. Concomitant pleural effusion and anaemia was thought to have caused the dyspnoea 2 years prior to presentation; subsequently, an additional dose of diuretics and a reduced dose of dasatinib (50 mg daily) resulted in a transient improvement of dyspnoea following a decrease in the amount of pleural effusion and a slight increase in haemoglobin without further evaluation. Electrocardiography and transthoracic echocardiography (TTE) on admission indicated severe right ventricular pressure overload. Physical examination showed jugular vein dilatation. His lung sounds were normal, but cardiac auscultation revealed increased intensity of the P2 sound. The liver was slightly enlarged, but splenomegaly was unclear. Laboratory data showed markedly elevated brain natriuretic peptide (442 pg/mL; normal reference value, <18.4 pg/mL), and anti-nuclear and anti-centromere antibody positivity (1280X and 166X, respectively). Contrast-enhanced chest computed tomography showed no evidence of pulmonary embolism, and perfusion-ventilation scintigraphy showed no evidence of segmental mismatch. Neither abdominal ultrasonography nor upper endoscopy showed clear evidence of portal hypertension. Right heart catheterization (RHC) confirmed markedly increased mean pulmonary artery pressure (MPAP; 67 mmHg; normal reference value, ≤20 mmHg) and pulmonary vascular resistance [PVR; 23.5 wood units (WU); normal reference value, ≤3 WU3] on room air. Because the patient presented with Raynaud’s phenomenon and nail fold bleeding, a skin biopsy was performed. Pathological findings included increased collagen fibres in subcutaneous adipose tissue and the dermis, increased mucin deposits between collagen fibres, and infiltration of inflammatory cells (mainly lymphocytes) around vessels, supporting a diagnosis of scleroderma. Neither DASA-PAH nor scleroderma-associated PAH (SSc-PAH) could be defined as the primary cause of PAH. Based on these findings, we simultaneously discontinued dasatinib and started initial combination therapy with the pulmonary vasodilators, tadalafil (40 mg daily), macitentan (10 mg daily), and selexipag (1.2 mg twice daily). RHC 1 month later showed improvement of the patient’s MPAP and PVR to 35 mmHg and 5.7 WU, respectively, with his 6-min walk distance also improving from 20 m to 490 m. RHC at 3 months demonstrated further improvement of MPAP and PVR to 33 mmHg and 3.9 WU, respectively. Serial TTEs performed at 1 and 3 months also revealed improved right ventricular pressure overload. At 4 months, as the Philadelphia chromosome became detectable, TKI administration with imatinib (300 mg daily) was resumed at a lower dose than previously prescribed. At 1 year, MPAP and PVR improved to reasonable values of 18 mmHg and 1.3 WU, respectively. We then withdrew selexipag from the treatment regimen without any evidence of clinical worsening.