3. Property and Equipment

Property and equipment are recorded at cost and depreciated over the estimated useful lives of the underlying assets (three to five years) using the straight-line method. As of September 30, 2019, and December 31, 2018, property and equipment consists of (in thousands):

Total depreciation and amortization expense were $24,000 and $69,000 for the three and nine months ended September 30, 2019, which includes amortization expense of $17,000 and $52,000 related to finance lease right-of-use lab equipment, respectively. Total depreciation and amortization expense were $11,000 and $40,000 for the three and nine months ended September 30, 2018, respectively, and included no amortization expense for finance lease right-of-use assets. For additional finance leases information, refer to Note 12 – Commitments and Contingencies.