Figure 1.

Model illustrating the implications of trastuzumab-resistant or trastuzumab-refractory disease. Disease progression while on trastuzumab correlates with intrinsic or primary resistance, whereas trastuzumab-refractory disease correlates with acquired or secondary resistance. Clinical scenarios in between represent a spectrum. In the adjuvant setting, progression while on or within a short period from trastuzumab likewise implies intrinsic resistance, but disease relapse after prior trastuzumab is heterogeneous and can fit into anywhere in the spectrum.

Abbreviation: T, trastuzumab.