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by Dr. C.H. Weaver M.D. updated 9/2019

Today three-month data from the ongoing Phase 3 VISTA Trial of Vicinium™ for the treatment of patients with high-grade non-muscle invasive bladder cancer (NMIBC) who have been previously treated with bacillus Calmette-Guérin (BCG) were released. Overall 43% of patients achieved a complete response and Vicinium appears to represent an emerging treatment option.

About Vicinium™

Vicinium™, also known as VB4-845, is an antibody-drug conjugate (ADC), developed for the treatment of high-grade non-muscle invasive bladder cancer (NMIBC). Vicinium is comprised of a recombinant fusion protein that targets epithelial cell adhesion molecule (EpCAM) antigens on the surface of tumor cells to deliver a potent protein payload, Pseudomonas Exotoxin A (ETA). EpCAM has been shown to be overexpressed in NMIBC cells with minimal to no EpCAM expression observed on normal bladder cells.

About Non Muscle Invasive Bladder Cancer

Bladder cancer is the sixth most commonly diagnosed cancer in the United States, and approximately 80 percent of patients have non-muscle invasive bladder cancer (NMIBC). In NMIBC, cancer cells are in the lining of the bladder or have grown into the lumen of the bladder but have not spread into muscle or other tissue.

Initial treatment includes surgical resection; however, there is a high rate of recurrence and more than 60 percent of all patients diagnosed with NMIBC will receive bacillus Calmette-Guérin (BCG) immunotherapy. BCG is an immunotherapy that is a weakened form of the bacterium related to bacteria causing tuberculosis. BCG is instilled directly into the bladder through the urethra and exerts its anti-cancer effect by stimulating the body’s immune system to kill cancer cells. Although BCG works in many patients, many will also eventually relapse. For those patients who relapse or who don’t respond at all, the standard alternative is radical cystectomy. In a cystectomy, the bladder is removed along with surrounding lymph nodes and other organs that contain cancer.

VISTA Trial Design

The Phase 3 VISTA clinical trial enrolled a total of 133 patients with high-grade NMIBC previously treated with BCG that were further characterized into 3 groups. Patients in the trial receive locally administered Vicinium twice a week for six weeks, followed by once-weekly treatment for another six weeks, then treatment every other week for up to two years.

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  • Group 1 (n=87): patients with carcinoma in situ (CIS) with or without papillary disease whose cancer recurred within six months of their last course of BCG treatment achieved a 39% response to treatment.
  • Group 2 (n=6): patients with CIS with or without papillary disease whose cancer recurred after six months, but before 11 months, after their last course of BCG treatment achieved a 80 percent response to treatment.
  • Group 3 (n=40): patients with papillary disease without CIS whose cancer recurred within six months of their last course of BCG treatment.

Three-Month Efficacy Results: CIS Patients

Vicinium treatment resulted in a complete response rate of 42 percent at three months.

At 12 months more than 75% of patients treated with Vicinium were estimated to remain cystectomy-free at 3 years, 90% were estimated to remain progression-free for 2 years or more and 29% were estimated to remain event free at 1 year.

The FDA had granted a fast track designation to Vicinium last August for the treatment of patients with BCG-unresponsive, high-grade NMIBC. References

  1. Sesen Bio Reports Positive, Preliminary Data Update from Phase 3 VISTA Trial for High-Risk Non-Muscle Invasive Bladder Cancer press release. Cambridge, MA: Sesen Bio; August 8, 2019. . Accessed August 9, 2019.
  2. Dickstein R, Wu N, Cowan B, et al. Phase 3 study of Vicinium in BCG-unresponsive non-muscle invasive bladder cancer: initial results. J Urol. 2018;199(4S; abstr LBA27):e1167. doi: 10.1016/j.juro.2018.03.099.
  3. Preliminary Data from Phase 3 VISTA Trial in Bladder Cancer to Be Presented in a Plenary Session at American Urological Association Annual Meeting