In these models, instead of 2D monolayers, cancer tumor cells are cultured as 3D spheroids. One of the benefits of the MCTS model is definitely that whenever spheroids reach a critical diameter, they begin to form an external proliferating zone, an inner quiescent zone, and a central necrotic core – more mimicking the microenvironments of human tumors faithfully. Additionally, spheroids can be grown in the current presence of substances that mimic extra cellular matrix – the environment that surrounds and very much affects the growth and behaviors of human being tumors.December 31 The upsurge in net loss due to common stockholders for the entire year ended, 2013 compared to the net loss due to common stockholders for the same period in 2012, was primarily because of $6.2 million of non-recurring noncash charges incurred during 2013 and one-time payments of $13.4 million received during 2012. In the first quarter of 2013, the Company's preferred share restructuring, which reduced the dividend requirements because of its Series A-1 preferred securities, led to a noncash charge of $2.9 million. In the next quarter of 2013, the Company retired its outstanding 8.0 percent senior secured convertible notes due August 2014 in the principal amount of $39 million producing a noncash lack of $3.3 million.