Participants will receive peginterferon alfa-2a subcutaneously in doses between 90 and 450 microgram (mcg) once weekly until medically indicated as judged by the treating investigator.

Peginterferon alfa-2a in doses between 90 and 450 mcg will be administered subcutaneously once weekly until medically indicated as judged by the treating investigator.

Hematologic response was considered to be achieved if participants met all of the following criteria: normalization of white blood cells count to less than (<) 10*10^9 per liter (/L) with normal differentiation, normalization of platelet count at <450*10^9/L, and disappearance of all signs and symptoms of the disease. This response had to be confirmed at least 4 weeks after the first measure and beyond that.

Time to loss of previous hematologic response was defined as the interval between the first day of treatment in the study and the first day of loss of previous hematologic response during elapsed time of study. Hematologic response was considered to be achieved if participants met all of the following criteria: normalization of white blood cells count to <10*10^9/L with normal differentiation, normalization of platelet count at <450*10^9/L, and disappearance of all signs and symptoms of the disease. This response had to be confirmed at least 4 weeks after the first measure and beyond that.

CyR was based on the prevalence of Philadelphia chromosome-positive (Ph+) bone marrow cells in metaphase determined from reverse transcriptase polymerase chain reaction (RT-PCR). Major cytogenetic response was categorized as either complete cytogenetic response (CCyR) or partial cytogenetic response (PCyR). CCyR was achieved when there was absence of detectable Ph+ bone marrow cells and PCyR was achieved when 1 to 34 percent (%) of bone marrow cells were Ph+.

Time to loss of previous CyR was defined as the interval between the first day of treatment in the study and the first day of loss of previous CyR. CyR is based on the prevalence of Ph+ bone marrow cells in metaphase. Major CyR was categorized as either CCyR or PCyR. CCyR was achieved when there was absence of detectable Ph+ bone marrow cells and PCyR was achieved when 1 to 34% of bone marrow cells were Ph+.

Participants who have previously participated in study ML16544, NO16006, or ML17228 and deemed to be a responder, received peginterferon alfa-2a subcutaneously in doses between 90 and 450 mcg once weekly until medically indicated as judged by the treating investigator. Maximum treatment duration was approximately up to 7 years.

Hematologic response was considered to be achieved if participants met all of the following criteria: normalization of white blood cells count to less than (<) 10*10^9 per liter (/L) with normal differentiation, normalization of platelet count at <450*10^9/L, and disappearance of all signs and symptoms of the disease. This response had to be confirmed at least 4 weeks after the first measure and beyond that.

Analysis population included all enrolled participants.

Participants who have previously participated in study ML16544, NO16006, or ML17228 and deemed to be a responder, received peginterferon alfa-2a subcutaneously in doses between 90 and 450 mcg once weekly until medically indicated as judged by the treating investigator. Maximum treatment duration was approximately up to 7 years.