Thanks for coming back to another edition of the Biotech Mailbag. Your comments and questions are most appreciated, so please keep them coming. You can email me here.

Chris M. is looking at other companies developing cancer vaccines, and he's stumbled across Antigenics ( AGEN - Get Report). "Volume is up and everything looks good, but going through its history -- yuck. What do you think?"

Yuck is right.

That pretty much sums up my view of Antigenics. Some investors are giving the company another look because of Dendreon ( DNDN). Antigenics' stock has gone from trading for less than $2 before Dendreon's Food and Drug Administration advisory panel to more than $4 soon after. (Antigenics shares closed Friday down 12 cents at $3.26.)

Look, I understand the desire to find the next cancer vaccine rocket ship, but Antigenics' drug Oncophage has barely risen off the launch pad, let alone made it to orbit.

Two phase III trials of Oncophage -- one in melanoma and another in kidney cancer -- failed. The company has attempted to cull positive data from various subgroups of patients in these trials, but the results, while positive, are not very reliable because all the work was done retrospectively.

It's worth noting, too, that Oncophage has had manufacturing problems. In the melanoma trial, for instance, there was a 30% manufacturing failure rate.

Most recently, Antigenics released positive data from a phase I/II study of Oncophage in brain tumor patients, but these results are early.

I understand the interest in Antigenics, but at this point, Oncophage is not ready for prime time.

Ben S. writes, "Adam, loved the Hepatitis C landscape article. In addition to figuring out who the market share winners will be, there seems to be quite a range in estimates of how big the Hep C market itself will ultimately be by 2010 and beyond. I've heard estimates from $5 billion to $10 billion. My understanding is that because of the virus' long incubation period, some doctors fear the disease may be very underdiagnosed. What kind of consensus on this topic do you sense out there?"

Great question, Ben. I think it's fair to say that the consensus on the size of the hepatitis C market is that it's quite large, as you indicated.

The World Health Organization estimates that 180 million people worldwide are infected with hepatitis C, 130 million of whom have chronic disease and are at risk of developing liver cirrhosis and/or liver cancer. Approximately 3 million to 4 million people are newly infected each year, according to the WHO.

Investors are focused more on the developed world, where all the new, groundbreaking hepatitis C drugs like Vertex Pharmaceuticals' ( VRTX - Get Report) telaprevir will be used. (That's a terrible statement, but sadly true.) In the U.S., the WHO estimates just under 4 million cases of hepatitis C infection, of which 70%, or 2.8 million, are chronically infected and candidates for treatment.

There are also about 400,000 chronic hepatitis C patients in the U.S. who have failed current treatment and are waiting for new, more effective drugs to try. These patients represent a huge potential windfall for the first drug company to make it to market with a new hepatitis C drug.

In Europe, the exact number of hepatitis C patients is less clear, but I've seen reports with estimates of between 5 million and 10 million infections, although the number of diagnosed patients is lower. Of course, the disease is also a big problem in Asia.

It's also worth noting that there are six different forms, or genotypes, of hepatitis C, with genotype 1 being the most prevalent in the Western world, and also the most difficult to treat. In the U.S., about 70% of hepatitis C patients are genotype 1.

With these kinds of patient numbers, it's not hard to get to the $5 billion to $10 billion market size estimates for hepatitis C. The wide range is attributable, in part, to the fact that we don't know what pricing for new drugs will look like, nor do we know yet how these new drugs will be used. But still, $5 billion to $10 billion is very big, so no wonder there is so much interest in hepatitis C stocks.

Richard A. read my Dor BioPharma ( DORB) item last week and asks what the estimated revenue value might be from the company's drug OrBec if it makes it to market.

I ran his question by a representative of Dor, who says the company projects OrBec peak revenue of about $87 million in the U.S., based on a 75% penetration rate of patients with acute, gastrointestinal graft-vs.-host disease. In Europe, peak revenue could reach $52 million, he said.

I'd be cautious with these estimates. They seem a bit high to me. For another perspective, I pulled up some sell-side research on Osiris Therapeutics ( OSIR), which is trying to develop a stem-cell therapy for acute GVHD. While not exactly comparable to Orbec, the revenue forecasts for this Osiris drug in GVHD range from $30 million to $60 million, so call it $45 million peak sales, average.

If Dor does manage to get Orbec approved, the company will try to expand the potential peak sales by studying the drug as a prophylaxis for GVHD, as well as for chronic GVHD. These are larger commercial opportunities.

Moving off your letters to end this column, I wanted to provide some quick updates on companies I've covered:

Flamel ( FLML): The Coreg CR launch by partner GlaxoSmithKline ( GSK) only kicked off in late March, so it's hard to accurately gauge success so far. That said, the early prescription trend data for Coreg CR that I've seen are encouraging.

Array BioPharma ( ARRY): Not a lot of news from its quarterly conference call. The company is in the process of raising money in a 7-million-share follow-on offering. The multiple cancer and inflammatory drug programs continue to move forward on schedule. A couple of new drugs should also enter human clinical testing later this year.

Exelixis ( EXEL): Reinitiated its study of XL999 in non-small cell lung cancer, as expected. The company reports first-quarter results next week, but the more relevant news will come later this year when we get new phase II data from a few of its cancer drugs.

Please note that due to factors including low market capitalization and/or insufficient public float, we consider Antigenics, Dor BioPharma and Osiris Therapeutics to be small-cap stocks. You should be aware that such stocks are subject to more risk than stocks of larger companies, including greater volatility, lower liquidity and less publicly available information, and that postings such as this one can have an effect on their stock prices.

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