Prostatic radioimmunoscintigraphy: preliminary results using technetium-labelled monoclonal antibody, CYT-351

To investigate the clinical application of a new technique for imaging prostatic malignancy using planar imaging and single-photon emission tomography (SPET) with technetium-99m-labelled antibody to a prostatic cell surface membrane antigen.

Prostatic malignancy was imaged by radioimmunoscintigraphy (RIS) using a 99mTc-labelled monoclonal antibody, CYT-351, raised against a newly identified membrane antigen present in normal and malignant prostatic tissues. The protocol involved taking serial images and assessing the changes in activity, as the uptake of specific antibody increased with time and non-specific uptake decreased. Data from planar images were collected at 10 min, 6 and 24 h after injection with antibody, and by SPET at 6 and 24 h using a Siemens Orbiter Large Field of View gamma camera. Twenty-two RIS scans were evaluated, which included six patients with clinically localized disease, six patients with previous incidental carcinoma at prostatectomy for apparently benign disease, four patients with evidence of local recurrence after radical prostatectomy and six patients with metastatic disease.

Primary tumours and secondary lymphatic and bone metastases were demonstrated. Only one minor side-effect was experienced.

This RIS technique was capable of imaging primary prostatic malignancy and metastatic disease in lymph nodes and bone. Its clinical application remains to be defined, but potentially it provides a new means for tumour staging based upon tissue characterization. It may be particularly useful before radical prostatectomy and it is capable of imaging local recurrence following radical treatment of localized disease. Future applications include monitoring the progression of disease and the response to treatment.