Shares of Affimed (AFMD -2.54%) have been soaring on the back of positive clinical trial results for an experimental cancer therapy that could be worth billions. The stock has already gained around 61% this year, but some biotech investors think it could climb much higher.

Can Affimed really make a millionaire out of the average investor? To find out, we'll need to look at what's driven the stock to recent peaks and what still needs to happen before it can make you rich.

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A revised approach

Affimed's heavily invested in a new approach to treating cancer that involves engaging a component of immune cells known as natural killer (NK) cells. The company's lead candidate at the moment, AFM13, is a two-faced antibody that binds to CD30, a protein often found on the surface of cancer cells, while its other side engages NK cells.

There are a lot of ins and outs when it comes to NK cells, but the important thing Affimed investors need to remember is that the cells can facilitate powerful immune responses to tumors. Getting them to attack cancer cells on command, though, has been more challenging than hoped.

Affimed initially began developing AFM13 as a relatively simple antibody, but the results were less than exciting. The company is back with an infusion of NK cells that are already bound to AFM13 and the new formulation appears to work like a charm. 

Why Affimed stock has soared

Shares of this biotech skyrocketed in April after the company showed investors impressive clinical trial results from the first few patients treated with AFM13-bound NK cells in a phase 1 dose determination study. Treatment with this version of AFM13 shrank tumors for all four Hodgkin's lymphoma patients treated so far.

Four out of four is a pretty good result for newly diagnosed lymphoma patients, but these trial volunteers already had lots of experience with different treatments. The least-experienced patient in the group had tumors that continued growing after four previous lines of therapy. Two of the four patients achieved complete remission after treatment with AFM13, including one who had been treated, unsuccessfully, with an experimental therapy made of CD30-directed T-cells.

So far, the new approach appears relatively well tolerated. Nasty side effects associated with other cellular cancer treatments haven't been observed among patients taking AFM13-bound NK cells.

Cellular cancer therapies like Yescarta from Gilead Sciences (NASDAQ: GILD) use specially engineered T-cells that were initially harvested from patients themselves. This convoluted process has limited their uptake, but this won't be an issue for AFM13. Instead of repeating a complex manufacturing process for each patient, Affimed can use AFM13 bound to a one-size-fits-all line of NK cells. 

Reasons to wait?

Using NK cells to facilitate an immune response around tumors that had previously avoided attention isn't a new concept. You should also know that initial successes with small patient groups have a disappointing tendency to drop off as cancer studies enroll more patients. 

The risk of cancer generally increases with age but it's also much harder to elicit responses from older patients. Four measurable responses from the first four patients dosed with a new candidate is an amazing start, but it's important to realize the oldest patient treated with AFM13 so far was just 53 years old.

As a clinical-stage biotech, Affimed doesn't have a reliable source of revenue yet. This means the company's $1.1 billion market cap could come crashing down if more recently enrolled patients don't exhibit similar responses.

Worth a shot

Affimed's market cap has swollen to 10 figures, but the stock at this price will seem like a terrific bargain if NK cells pre-complexed with AFMD13 continue to impress. Until we see confirmation from more patients, though, investors want to approach this stock with caution.

This biotech has what it takes to make millionaires out of everyday investors. Just be sure to keep shares of its still-risky stock in a well-diversified portfolio.