Exact copies of originator biopharmaceuticals are impossible to produce due to the previously mentioned complexity and inherent heterogeneity they possess. A biosimilar can be described as a copy of an already authorized biological medicinal product which demonstrates similarity in physicochemical characteristics, efficacy, and safety, based on a comprehensive comparability exercise.  Biosimilar manufacturers must develop their own manufacturing process with the ability to produce a product as similar to originator as possible due to the originator's reference material and manufacturing process being proprietary.
The quality attributes of the biosimilar and the originator will be different due to differences in the manufacturing process. This is to be expected and is not a matter of concern as it has been accepted as par for the course for biopharmaceutical production. Such differences can arise from variations in expression systems, fermentation and purification processes, and the use of excipients. 
In contrast to traditional small molecules where identical copies of the originator drug are possible, the standard generic approach of establishing bioequivalence via competitive bioavailability studies is insufficient. A biosimilar's critical quality attributes are assessed by clinical studies where their physicochemical properties, safety and efficacy are tested for comparability against the originator. A biosimilar may also be exposed to non-clinical assessment if deemed necessary. The repeating of phase I and III clinical trials, and thereby enrolment of several hundred patients, has led to a recent study putting estimated clinical costs alone at $8.5-35 M compared with a total cost of $5 M for developing a generic small molecule drug. [6,7]
Again, in contrast to small molecules where an 80% reduction in price can be expected following release of generic product(s), the same cannot be said for biopharmaceuticals.  The regulatory framework is currently much more established in Europe than in the US with an excess of 15 biosimilars already on the market. 
This includes the first monoclonal antibodies (mAbs) Remsima and Inflectra (Infliximab/Remicade), which gained approval in 2013.