For the six months ended June 30, 2020, the decrease in ciforadenant costs of $1.0 million as compared to the six months ended June 30, 2019, primarily consisted of a decrease of $0.5 million in clinical trial expenses, a decrease of $0.3 million in drug manufacturing costs and a decrease of $0.2 million in other outside services.
For the three months ended June 30, 2020, the decrease in CPI-006 costs of $0.5 million as compared to the three months ended June 30, 2019, primarily consisted of a decrease of $1.7 million in drug manufacturing costs, partially offset by an increase of $1.1 million in clinical trial expenses and an increase of $0.1 million in other outside services.
For the six months ended June 30, 2020, the increase in CPI-006 costs of $1.1 million as compared to the six months ended June 30, 2019, primarily consisted of an increase of $2.5 million in clinical trial expenses and an increase of $0.2 million in other outside services, partially offset by a decrease of $1.6 million in drug manufacturing costs.
For the three months ended June 30, 2020, the decrease in CPI-818 costs of $0.7 million as compared to the three months ended June 30, 2019, primarily consisted of a decrease of $0.5 million in drug manufacturing costs and a decrease of $0.2 million in other outside services.
For the six months ended June 30, 2020, the decrease in CPI-818 costs of $1.6 million as compared to the six months ended June 30, 2019, primarily consisted of a decrease of $1.4 million in drug manufacturing costs and a decrease of $0.2 million in other outside services.
For the three months ended June 30, 2020, the decrease in other program costs of $0.1 million as compared to the three months ended June 30, 2019, primarily consisted of a decrease in outside services.
For the six months ended June 30, 2020, the increase in other program costs of $0.2 million as compared to the six months ended June 30, 2019, primarily consisted of an increase of $0.5 million in drug manufacturing costs, partially offset by a decrease of $0.3 million in outside services.
For the three months ended June 30, 2020, the decrease in unallocated costs of $0.7 million as compared to the three months ended June 30, 2019, primarily consisted of a decrease of $0.6 million in outside services and a decrease of $0.1 million in personnel and related costs.
For the six months ended June 30, 2020, the decrease in unallocated costs of $0.8 million as compared to the six months ended June 30, 2019, primarily consisted of a decrease of $0.9 million in outside services, partially offset by an increase of $0.1 million in personnel and related costs.
General and Administrative Expense
For the three months ended June 30, 2020, the negligible decrease in general and administrative expenses as compared to the three months ended June 30, 2019, primarily consisted of an increase of $0.4 million in professional service costs, offset by a $0.4 million decrease in stock-based compensation expense.
For the six months ended June 30, 2020, the increase of $0.2 million in general and administrative expenses as compared to the six months ended June 30, 2019, primarily consisted of an increase of $0.7 million in professional service costs, offset by a $0.4 million decrease in stock-based compensation expense and a decrease of $0.1 million in other personnel related costs.
Interest Income and Other Expense, net
For the three months ended June 30, 2020, the decrease in interest income and other expense, net of $0.5 million as compared to the three months ended June 30, 2019, primarily consisted of a decrease in interest income earned due to a decrease in cash equivalents and marketable securities and a decrease in interest rates.