Intraductal carcinoma of the prostate (IDC-P) gland represents an intraluminal neoplastic proliferation that is distinct from high-grade prostatic intraepithelial neoplasia (HG-PIN) and almost always coexists with large-volume, high-stage, and high-grade invasive carcinoma. We document an unusual presentation of apparently "early" IDC-P without an aggressive invasive element that, despite being confined to the acinar-ductal system, has gained access to the ejaculatory duct and seminal vesicle by transmucosal spread. This finding confirms that IDC-P, in contrast to HG-PIN, is inherently aggressive and has the ability to spread beyond the prostate gland. In this case, the absence of an aggressive invasive element suggests that IDC-P has most likely evolved within the lumens directly from HG-PIN.