CHICAGO (TheStreet) -- The knock on ImmunoGen (IMGN) - Get Report has long been that early success with its "smart bomb" cancer drug delivery technology wasn't being replicated. At this weekend's ASCO meeting, however, the company's lead pipeline drug IMGN853 posted impressive responses in a segment of hard-to-treat ovarian cancer patients.

The perception that ImmunoGen can't develop a drug successfully on its own will probably improve Monday when post-ASCO trading kicks in.

Buoyed by the results presented at the ASCO meeting this weekend, ImmunoGen plans to launch a study later this year which, if positive, could be used to seek approval of IMGN853 as a treatment for advanced ovarian cancer.

IMGN853 consists of a monoclonal antibody designed to seek out and attach itself to tumors with large quantities of a protein, folate receptor alpha, on their surface. The IMGN853 antibody carries a toxic chemotherapy payload, which is released into the tumor once attached.

The analysis of a phase I study presented on Saturday, encompassed 22 women with folate-positive ovarian cancer that had grown resistant to standard, platinum-based chemotherapy. The median number of prior ovarian cancer treatment regimens was four, with some patients undergoing as many as 12 prior treatments.

Among the 17 patients evaluable for efficacy, the response rate to IMGN853 was 53%, including one complete response and eight partial responses. When ASCO abstracts were released two weeks ago, the IMGN283 response rate was 40%.

While only a small number of patients were analyzed, the IMGN853 response rate compares well to response rates in the 20% range typically seen from various chemotherapy regimens used in heavily pre-treated ovarian cancer patients.

Roche's (RHHBY) Avastin plus chemotherapy, approved to treat recurrent, platinum-resistant ovarian cancer, demonstrated a response rate of 28%, although the patients had no more than two prior lines of therapy prior to enrolling in the study.

From a safety perspective, the biggest concern with IMGN853 is blurred vision, which occurred in approximately half of the patients analyzed in the ImmunoGen study. The blurred vision was characterized as mild to moderate and managed by reducing or delaying the IMGN853 dose. One patient discontinued treatment with IMGN853 due to blurred vision.

Each year, there are approximately 21,300 new cases of ovarian cancer diagnosed in the US and more than 14,200 women die from the disease. ImmunoGen estimates that approximately 2,000-3,000 of these women have folate-receptor-positive, platinum-resistant ovarian cancer previously treated with at least three prior lines of therapy. This will be the target patient population for the next clinical trial of IMGN853 expected to start before the end of the year.

ImmunoGen's antibody-drug conjugate (ADC) technology was incorporated into Kadcyla, a breast cancer drug developed and brought to market successfully by Roche. Since then, however, ImmunoGen has struggled. The development of other partnered drugs has been slow or delayed due to dosing and safety issues, while ImmunoGen's own pipeline has progressed more slowly than previously expected.

For these reasons, IMGN853 is both welcomed and much needed by ImmunoGen.

Adam Feuerstein writes regularly for TheStreet. In keeping with company editorial policy, he doesn't own or short individual stocks, although he owns stock in TheStreet. He also doesn't invest in hedge funds or other private investment partnerships. Feuerstein appreciates your feedback; click here to send him an email.