West Asia Organization for Cancer Prevention (WAOCP), APOCP's West Asia Chapter. Asian Pacific Journal of Cancer Prevention 1513-7368 24 2 2023 02 01 The Metastatic Spread of Breast Cancer Accelerates during Sleep: How the Study Design can Affect the Results 353 355 90512 10.31557/APJCP.2023.24.2.353 EN Mohammad Houshyari Department of Clinical Oncology, Shahid Beheshti University of Medical Sciences, Tehran, Iran. Farzad Taghizadeh-Hesary ENT and Head and Neck Research Center and Department, The Five Senses Health Institute, School of Medicine, Iran University of Medical Sciences, Tehran, Iran. Department of Radiation Oncology, Iran University of Medical Sciences, Tehran, Iran. 0000-0002-6195-2203 Journal Article 2023 02 04 Metastasis is the most common event that determines survival in patients with breast cancer. The benefits of appropriate sleep in enhancing cancer patients' prognosis have been demonstrated. Likewise, emerging evidence has noted the positive impacts of regular circadian rhythm on cancer survival. Proper sleep and regular circadian rhythm can help to improve the cancer prognosis by enhancing the immune system. Besides, circadian rhythm disruption can assist cancer progression by promoting systemic inflammation. However, a recent study by Diamantopoulou et al. titled “The Metastatic Spread of Breast Cancer Accelerates during Sleep” demonstrated that sleep can aggravate breast cancer metastasis. This article outlines how the study design can affect this controversy. https://journal.waocp.org/article_90512_7b7352bc67336a1dc562f3e6de65eb69.pdf