Step 3: After an immunotherapy makeover, CytomX files $100M IPO

After remaking its pipeline to fit one of the hottest fashions in biotech and engineering a classic $70 million crossover round, South San Francisco-based CytomX is taking the inevitable next step with a $100 million IPO filing.

CytomX is once again testing just how adventurous investors are feeling these days. It has a long lineup of preclinical projects in the pipeline, but nothing that's reached humans yet. For much of the past three years, the absence of data may not have posed a big problem, but recent market turmoil may have started to change attitudes about risk and stock portfolios.

The biotech's new lead program is for PD-L1, targeting the darling of the immuno-oncology space, which has been focused on dismantling the barrier between cancer cells and T cell attackers. There are already a pair of complementary PD-1 drugs--Opdivo and Keytruda--on the market. And Roche ($RHHBY) and AstraZeneca ($AZN) are coming along with late-stage efforts for PD-L1, followed by a steadily growing pack of players anxious to stake a claim in the multibillion-dollar market now being created. 

CytomX's CX-072 won't even be ready for an IND filing until the second half of 2016. But even with the late start, the biotech believes it has an inside track at a new-and-better technology.

The company's story centers closely on its antibody design, which they have dubbed Probodies. Its antibodies are designed with tips that let them slide past healthy tissue until they reach a tumor microenvironment, where proteases clip off the end and let them go to work on cancer cells. By doing that, the biotech believes it can come up with a safer approach that avoids triggering side effects, such as an autoimmune response. There's also an antibody drug conjugate in play as well as a CTLA-4 effort partnered with Bristol-Myers Squibb ($BMY), the leader in immuno-oncology today, which came with a $50 million upfront.

Getting to this stage cost $92.6 million (there's $125 million in cash), according to the S-1, and lots more money is needed before Phase III arrives.

Attracted by its potential, Pfizer ($PFE) signed early on as a partner in a heavily back ended $610 million deal, with $530 million built around sales milestones. And ImmunoGen is also partnered with the company, a 2013 Fierce 15 biotech.

According to the S-1, Third Rock is still the big investor, with 31% of the stock. Canaan comes in at 17% followed by Fidelity Management and Research at 8.7%. CytomX is the latest in a series of Third Rock companies to hit the IPO queue this year.

- here's the S-1

Special Report: FierceBiotech's 2013 Fierce 15 - CytomX