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Do Organovo Holdings (ONVO -4.35%) and MannKind Corp. (MNKD 2.45%) compete against each other? Not on the surface. The two healthcare stocks have similar market caps, but seemingly little else in common. Organovo develops 3D bioprinted human tissues, while MannKind's core product is Afrezza, an inhaled form of insulin.

In one sense, though, Organovo and MannKind do compete against each other. Every dollar you invest in one stock is a dollar that you can't put into another stock. Every stock on the market competes for investors with every other stock.

With that perspective in mind, which of these stocks is the better buy? The answer, as is usually the case with comparisons between two investment alternatives, comes down to risk versus reward. 

Potential risks

Organovo's biggest risk is that the market for its products takes too long to mature. Some potential customers remain skeptical about the value of 3D bioprinted tissues and prefer to keep using 2D tissues or testing with animals.

That skepticism shows up in Organovo's financials. The company reported revenue last quarter of less than $1 million, even though its first product, exVive3D bioprinted human liver tissue, has been commercially available since November 2014.

The good news for Organovo is that it had $53.5 million in cash and cash equivalents at the end of its fiscal first quarter ending June 30, 2016. The bad news is that the company projects it will burn through as much as $36.5 million this fiscal year. Sales don't appear likely to climb fast enough for Organovo to avoid another public stock offering, which would dilute the value of existing shares.

What about MannKind's primary risk? It's pretty much the same as for Organovo, except the situation looks even worse. Afrezza has been on the market since February 2015. Sales for the inhaled insulin in the last quarter totaled... well, there was no sales revenue reported by MannKind. Sanofi was MannKind's marketing partner on the drug, and Sanofi threw in the towel on Afrezza in January after less than a year of disappointing commercial results.

MannKind reported cash and cash equivalents of $63.7 million at the end of June. That amount won't last long. The company has lost nearly $30 million in each of the first two quarters this year. MannKind does have a few options at its disposal to generate more cash, though: There's another $30.1 million available for borrowing under an existing loan agreement. MannKind could also raise another $50 million through an at-the-market (ATM) financing facility.   

Potential rewards

The bright side for Organovo continues to be the potential for its technology. Organovo's management team thinks that exVive3D has revenue potential of over $100 million annually. The company is launching its second product later this year, a 3D bioprinted human kidney tissue.

Are Organovo's expectations attainable? Maybe. There's reason to believe that some of the initial skepticism about 3D tissues could be waning. Organovo added another couple of large drugmakers to its customer base last quarter, bringing the count of customers in the top 25 biggest pharmaceutical companies to seven overall.

While revenue is still small, it's growing quickly. At current growth rates, Organovo could possibly reach break-even status within the next three years.

As for MannKind, the news could possibly improve in the near future. The biotech plans to relaunch Afrezza in September. MannKind's chief commercial officer, Michael Castagna, said in the company's second-quarter conference call that several steps are being taken to increase the chances of a successful launch, including a new branding focus and direct-to-consumer marketing.

It probably wouldn't take huge sales for Afrezza to generate a spark for MannKind. If the company could get any kind of momentum going, MannKind would likely become one of the biggest biotech comeback stories in recent history.

Better buy

Both of these stocks remain very risky. I'd say the better buy, though, is Organovo.

The market seems to be coming around at least to some extent for exVive3D. It's still early, but I suspect Organovo's sales growth will continue to be strong. The company has upped its game in getting the word out about the value of 3D bioprinted tissues through scientific publications. That helps.

I'd love to see MannKind make a historic comeback from the near-dead. However, the company faces huge challenges ahead. In my view, Organovo has the better risk-versus-reward profile right now.