15 . Commitments and contingencies Operating leases At December 31, 2017, the Company leases facilities under six non-cancelable operating leases, with terms that expire between 2018 and 2025. The Company leases office, storage/warehouse, laboratory and manufacturing space in Abingdon, U.K., which leases are due to expire on January 31, 2025 ( with respect to the storage/warehouse facility) and June 11, 2019. On March 1, 2013, the Company signed a five year lease for its U.S. corporate headquarters in Marlborough, Massachusetts. In August 2015, the Company entered into a lease amendment for this location to extend the term of the lease by two years through October 31, 2020. In addition, the lease amendment expanded the Companys office space at this location by 7,600 square feet to a new total of 22,100 square feet. The base rent for the combined space over the lease term will range from an initial low of $36,000 per month, which includes $12,000 per month for the expansion space commencing in early 2016, to a high of $39,000 per month. The Company will have an option to extend the lease for one additional term of five years. In addition, the Company leases laboratory space in Memphis, Tennessee, which lease is due to expire on December 31, 2021. The Company has an option to extend the lease for two additional terms of five years each. The two laboratory facilities acquired in 2016 are located in Norwood and Boston, Massachusetts. The Company currently leases approximately 58,000 square feet of space in Norwood and approximately 18,000 square feet in Boston. The Norwood lease expires in 2023, while the Boston lease expires in 2018. The Companys current rent under the Norwood lease is $975,000 annually, subject to annual increases. The Companys current rent under the Boston lease is $263,000 annually. Future minimum lease payments required under the non-cancelable operating leases in effect as of December 31, 2017 are as follows: (in thousands) December 31, 201 7 201 8 $ 1,957 201 9 1,595 2020 1,429 2021 664 202