Immunomedics' blood assay for PAM4-protein can detect pancreatic cancer and predict early relapse

• Sensitivity for Detection of a Partial Response (PR) was 100% with a 68% Specificity
• Preclinical Results of Combining Clivatuzumab Tetraxetan and Antibody-Drug Conjugate also Reported

Immunomedics, Inc. (Nasdaq:IMMU), a biopharmaceutical company focused on developing monoclonal antibodies to treat cancer and other serious diseases, today reported that a new blood test using the Company's proprietary humanized antibody, clivatuzumab or PAM4, predicted a partial response in an initial set of patients treated with a combination of the antibody labeled with yttrium-90 (Y-90) and gemcitabine. Results were presented at the 101^st Annual Meeting of the American Association for Cancer Research.

"We have now demonstrated that the blood assay for PAM4-protein can not only detect early-stage pancreatic cancer, as has recently been reported by us, but may also predict a lack of response to therapy or an early relapse," remarked Cynthia L. Sullivan, President and CEO. "As a result, we believe we may be one step closer to offering an individualized approach for the management of this lethal disease," Ms. Sullivan added.

The challenge in pancreatic cancer is early diagnosis, before the disease has spread and treatment options become limited. To that end, the Company has recently developed a new serum-based enzyme immunoassay (ELISA) employing clivatuzumab that has a sensitivity of 62% for detecting stage-1 pancreatic cancer (disease confined to pancreas), 86% for stage 2 disease, and 91% for stage 3/4 (local and distant spread) cancers.  (Please refer to the Company's press release at www.immunomedics.com/news_pdf/2010_PDF/PR01212010.pdf for details of these results). Using the same ELISA test, the current study examined changes in PAM4-protein level in the serum of patients treated with Y90-clivatuzumab, as a means to predict a partial response.

At the recent 2010 ASCO-GI Symposium, the Company reported an overall response rate of 68% with 5 patients having a partial response (PR), 10 with stable disease (SD) and 7 with progressive disease (POD). (For more information on the Phase I/II studies of clivatuzumab as a treatment for patients with pancreatic cancer, please refer to the Company's press release at www.immunomedics.com/news_pdf/2010_PDF/PR01252010.pdf). From this initial group of 22 patients, 17 were evaluable as having both baseline and follow-up sera available for PAM4 testing, of which 4 were PR, 11 patients with SD and 2 patients with POD. Notably, 1 patient was negative for PAM4 in the circulation and excluded from the evaluation.

The PAM4 ELISA correctly predicted 4 of 4 PRs. Four of 9 patients with SD were also predicted to have had a PR rather than an SD. However, it is noted that one of these SD patients had a 29% decrease in tumor size which is just under the 30% criteria under RECIST to qualify as a PR. Overall, the sensitivity for detection of a PR was 100% with a specificity of 68%. Importantly, neither of the patients with POD was falsely recognized as PR. 

"Although these results are based on a small number of patients, the trend encourages us to expand such studies to evaluate whether this new bioassay for pancreatic cancer continues to be predictive of response to diverse therapies," Ms. Sullivan commented further.

Separately, in a study to be reported later in this conference, the effects of adding an antibody-drug conjugate that targets pancreatic cancer (hRS7-SN-38) to Y-90 labeled Clivatuzumab tetraxetan were investigated in a mouse model of human pancreatic cancer. Results showed that the combination produced more robust objective response than each agent alone. In particular, all animals receiving Y90-clivatuzumab at the maximum tolerated dose and hRS7-SN-38 achieved a tumor-free state within 4 weeks, while other animals continued to have evidence of persistent disease. These studies provide the first evidence that combined radioimmunotherapy and antibody-drug conjugate can enhance efficacy at safe doses.