NEW YORK (TheStreet) -- It's a day that ends in "day," which means cancer immunotherapy is dominating the biotech news.

The answer to almost every Sanofi (SNY) - Get Report question about drug research and development appears to be, "Just write a big check to Len."

Len is Leonard Schleifer, CEO of Regeneron Pharmaceuticals , the large-cap biotech company which also serves as struggling Sanofi's de facto drug developer.

On Tuesday, the two companies paired up again, this time in a big-money collaboration to develop new cancer immunotherapies. Financial terms of the deal can be found here, but all you really need to know is that Sanofi badly trails its Big Pharma brethren in developing drugs that harness a patient's immune system to target and kill cancer cells.

While Bristol-Myers Squibb (BMY) - Get Report, Merck (MRK) - Get Report and Roche (RHHBY) lead the way in the development of checkpoint inhibitors and other cancer immunotherapies, Sanofi has done essentially nothing. Sanofi is desperate, so now it's paying huge sums of cash to Regeneron, hoping to catch up in cancer.

In yet another illustration of the investment mania for all things cancer, biotech billionaire Patrick Soon-Shiong's latest business venture makes its public debut Tuesday as the largest biotech initial public offering ever. [The previous "largest biotech IPO ever" was Alzheimer's play Axovant Sciences (AXON) - Get Report, which is now trading below its offering price.]

NantKwest (NK) - Get Report priced 8.3 million shares at $25 per share, raising $207 million and valuing the cancer immunotherapy company at $2.6 billion. The IPO was 25 times over-subscribed, according to a healthcare investor who put in for an allocation. Early reports showed that NantKwest will open at $35 per share.

If you must know, NantKwest is developing drugs which aim to harness the body's "natural killer" cells to find and kill tumors. The company's work is early, highly speculative and probably way over-valued by the market already, but investors are likely more drawn to the company's IPO because of the involvement of Soon-Shiong, the "world's richest doctor" and a billionaire many times over thanks in large part to a cancer drug called Abraxane which he sold to Celgene (CELG) - Get Report for almost $3 billion.

Few people knew about NantKwest last year when it was known as Conkwest, but then Soon-Shiong invested, took over as CEO and plugged the rebranded company into his intermingled (and confusing) network of "Nant" healthcare and technology businesses.

I'm sure the bankers' investor pitch for NatKwest went something like this, "Don't worry about what they do, it's Patrick Soon-Shiong. How much do you want?"

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.