A prime cancer vaccine comprised of a genetically engineered, replication-deficient adenovirus serotype 26 (Ad26) encoding the oncogenic human papillomavirus 18 (HPV18), with potential immunostimulating and antineoplastic activities. Upon intramuscular administration of Ad26-expressing HPV18 vaccine JNJ-63682931, the adenovirus infects and expresses HPV18. The expressed proteins stimulate the host immune system to mount a cytotoxic T-lymphocyte (CTL) response against tumor cells expressing HPV18 antigens, thereby inducing tumor cell lysis. HPV18 infection plays a key role in the development of a variety of cancers.