Can a DNA vaccine train the immune system to hunt down HER3-Positive cancers?

Copied word for word from the study's registry entry, so the wording is the study team's rather than ours.

Inclusion Criteria: * Documented history of solid tumor where HER3 expression is expected (this includes breast, colon, lung, prostate, ovarian, cervical, endometrial, gastric, pancreatic, bladder, head and neck, liver, and esophageal cancer, but other tumors will be considered based on emerging HER3 expression data in the literature). Demonstration of HER3 expression is not required for enrollment. * Has undergone surgical resection of malignancy and has completed intended standard course of chemotherapy and HER2 targeted therapy and radiotherapy under the direction of their physician. Subjects may continue on adjuvant hormonal therapy. * Has no evidence of disease by standard imaging studies (performed at the direction of their physician) within 60 days prior to initiating study treatment. * Between 3 weeks and 2 years since prior cytotoxic chemotherapy, HER2-targeted therapy or radiotherapy to the start of study treatment. * ECOG 0 or 1 * Estimated life expectancy \> 3 months. * Age ≥ 18 years. * Adequate hematologic function, with ANC \>1500/µL, Hemoglobin ≥ 9 g/dL, and Platelets ≥ 75,000/µL. * Adequate renal and hepatic function, with Serum Creatinine \< 1.5 mg/dL, Bilirubin \< 1.5 mg/dL (except for Gilbert's syndrome which will allow bilirubin ≤ 2.0 mg/dL), ALT and AST ≤ 2.5 x ULN or if liver metastases are present \< 5 x ULN. * Female patients must be of non-child-bearing potential or use effective contraception, . * Labs performed as standard of care prior to signing consent can be used to fulfill eligibility requirements if they were performed within 4 weeks of the start of study treatment. * Ability to understand and provide signed informed consent. * Ability to return to the study site for adequate follow-up, as required by this protocol. * Negative serum pregnancy test within 7 days prior to the start of study treatment, for women of childbearing potential only. Exclusion Criteria: * Patients must have recovered to Grade 1 toxicities from any prior treatment(s). * Known CNS/brain metastases * History of auto-immune disease such as, but not restricted to, inflammatory bowel disease, systemic lupus erythematosus, ankylosing spondylitis, scleroderma, or multiple sclerosis. * Serious chronic or acute illness considered by the Principal Investigator to constitute an unwarranted high risk for investigational treatment. * Medical or psychological impediment to probable compliance with the protocol. * Concurrent or prior second malignancy (within the past 5 years) other than non-melanoma skin cancer, Carcinoma in situ of the bladder and cervix. * Presence of active infection or systemic use of antimicrobials within 48 hours prior to the start of study treatment. * Patients on continuous steroid therapy for at least 72 hours (or other continuous immunosuppressives such as azathioprine or cyclosporine A) are excluded on the basis of potential immune suppression. * Presence of a known active acute or chronic infection including HIV or viral hepatitis (Hepatitis B and C). * Pregnant or nursing women. * Prior immunotherapy