We present resistive pulse and optical data of cancer cells deforming while passing through microsized constrictions. Cell stiffness, the degree to which cells deform under strain forces, is known to be an important physical parameter that along with other physical and chemical biomarkers can be used to differentiate cell types and enable clinical detection of cancerous cells. Many desirable applications, such as detecting metastatic circulating tumor cells, rely on a high throughput of measurements, since the specimen of interest may comprise only a total fraction of the total number of particles in a sample. Capable of measuring 1000s of cells/sec, real-time flow deformability cytometry is a high throughput method for determining a cell's stiffness that works by inducing cell deformation under strain forces in the pressure-driven laminar flow through a microfluidic channel. Currently, real-time flow deformability cytometry relies on taking high-speed camera data of the sample, which is expensive to acquire and analyze. We propose to measure cell stiffness using resistive pulse sensing, whereby a particle's physical properties are measured from the change in the transchannel electrical current during the particle's transit. By using a microfluidic channel with regions differing in diameter, the particle is deformed to different degrees, distorting the resistive pulse signal relative to the signal expected of a hard sphere. We show resistive pulse data taken of hard spheres and cells with varying degrees of deformability, and using high speed video, show cells deforming in the channel.