This paper concerns the design of in-band fullduplex transceivers that employ generalized frequency-division multiplexing (GFDM). The composite of these two timely concepts is a promising candidate technology for emerging 5G systems since the GFDM waveform is advantageous to flexible spectrum use whereas full-duplex operation can significantly improve spectral efficiency. The main technical challenge in fullduplex transceivers at large is to mitigate their inherent self-interference due to simultaneous transmission and reception. In the case of GFDM that is non-orthogonal by design, interference cancellation becomes even more challenging since the interfering signal is subject to intricate coupling between all subchannels. Thus, we first develop a sophisticated frequency-domain cancellation architecture for removing all the self-interference components. Furthermore, by exploiting the specific structure of the interference pattern, we further modify the scheme into one that allows flexible control and reduction of computational complexity. Finally, our simulation results illustrate the trade-off between cancellation performance and system complexity, giving insights into the implementation of interference cancellation when we aim at achieving both low error rate and low complexity.