Prostate cancer masquerading as a large rectal cancer: diagnosis by endoscopic ultrasound

Abstract

A 76-year-old man underwent evaluation for a 2-week history of decreased stool frequency, intermittent mild abdominal pain, and occasional nausea and vomiting. He denied weight loss, hematochezia, fever, or change in urinary function. Physical examination revealed normal bowel sounds without hepatosplenomegaly. Mild suprapubic tenderness was present. By digital rectal examination, a large mass was palpable in the rectal vault that was fixed both anteriorly and posteriorly. Colonoscopy revealed an annular, firm, and friable mass, 5 cm in length, beginning at 16 cm above the exterior anal verge. The mass appeared to be intrinsic to the bowel wall by visual inspection, with prominent central ulceration (Fig. 1). The remainder of the examination was unremarkable except for several small diverticula in the transverse colon. Preliminary pathologic review suggested a poorly differentiated adenocarcinoma of rectal origin. EUS was done for local staging to determine the need for neoadjuvant therapy. A radial scanning echoendoscope (GFUM-20; Olympus America, Inc., Melville, N.Y.) was used with a water-filled balloon and instillation of water into the rectum. Ultrasound scanning was performed at 7.5 MHZ to 9, 6, and 4 cm depths. EUS revealed a 6 × 4 cm hypoechoic mass extrinsic to the bowel wall. The tumor was noted to penetrate the four outermost ultrasonographic layers of the rectal wall, including the hypoechoic muscularis mucosa. The innermost hyperechoic layer, representing the balloon-mucosa interface, remained intact for the majority of the length of the tumor, although this layer was deformed by the underlying mass (Fig. 2). Approximately one half of the prostate gland was replaced with an irregular, echopoor lesion that obliterated and extended beyond the external capsular border. A hypoechoic tongue of tumor arising from the prostate communicated with the extrinsic bowel wall mass (Fig. 3). Multiple hypoechoic lymph nodes larger than 1 cm in diameter were seen above the tumor mass. These findings suggested a primary prostate carcinoma, with bowel wall invasion and local nodal metastases, mimicking a rectal neoplasm. Histopathologic study confirmed the prostatic origin of the tumor. Hematoxylin and eosin–stained sections of the rectal biopsy revealed a poorly differentiated tumor infiltrating the submucosa and muscularis mucosae. The mucicarmine stain was negative for mucin. Immunohistochemical stains revealed intracytoplasmic staining of the neoplastic cells with prostate specific antigen. Hormonal therapy with flutamide and leuprolide was initiated, with good response.