ERBB2 and squamous cell carcinoma: Measurements of phosphorylated HER1, while not as prevalent in the majority of HER2-positive breast tumors, may also aid in prediction of response to targeted therapies in de novo or acquired Herceptin-resistant breast cancers as well as multiple additional cancer types, including squamous cell carcinoma of the head and neck, lung, gastric, and triple-negative breast cancers [65-71].