Plexin-B1 is expressed in neurotropic tumors, whereas nerves express Sema4D. A: IHC analysis for plexin-B1 in normal tissues, tumors not known to exhibit PNI, or benign controls (low-PNI tumors/benign controls), and tumors known for PNI (high-PNI tumors), grouped by site of origin, either mucosa, salivary gland, or prostate. HNSCC, high-grade MEC, ACC, PLGA, and prostate cancers demonstrate abundant plexin-B1 staining. Original magnification, ×20. B: Cross section of a nerve showing expression of Sema4D. Original magnification, ×20. C: A scale of 0 to 3 was used to assess the number of positively stained cells and the staining intensity for plexin-B1 in the high-PNI tumor groups shown. These two scores were added together to yield the ranges shown in the pie charts.