For readers who have not been following our newsletter editors for an extended period, it’s time to acquaint you with a longstanding policy: We never buy a stock for one of our portfolios for 2 trading days after you read about it. This means we’ll never front-run a stock, getting in before the crowd as many “pump and dump” financial advisory firms do. It also means we hamstring our performance — if readers decide to buy our picks and push them up in value before we can get in.

This lesson was brought home to us this week. I started to prepare an article highlighting the merits of biotech pick Celsion (Nasdaq: CLSN) when shares were trading at $3.25. By the time this article appeared on our site, shares were already up to $3.88. And by the time I bought shares on Monday, Aug. 20, they had risen to $4.29. That’s a 30% gain since I first decided to add it to the portfolio last week.

Make no mistake, I would have decided to cancel the trade, waiting for a better entry point — if I thought one was coming. But I don’t. Even at current prices, I still think this stock has significant upside (though as I’ll explain in a moment, there is plenty of downside as well).

I initially planned to buy 2,000 shares, which would mean I would have committed more than $8,000 to what is a speculative play. So I decided to trim the purchase to 1,500 shares, or roughly $6,400.#-ad_banner-#

As I noted last week, there are a series of drivers in place for this stock that the current $140 million market value doesn’t begin to reflect. I am loathing to say how high this stock can go, because there are so many variables in place. Shares have gotten recent support from research firm Griffin Securities, which has an $18 price target in place. I think that’s a bit irresponsible. That target implies everything going right for Celsion, and in the world of biotech, the stars rarely come into perfect alignment.

It may be helpful anyway to see why analysts at Griffin Securities arrive at that price target. They apply a price-to-earnings (P/E) multiple of 30 on projected 2015 earnings of 92 cents per share (using a 24% discount rate). They see shares garnering that multiple 12 months from now, which works out to their $17.95 price target.

A few other comments about Griffin’s outlook:

• Although I believe that Celsion’s fast-track approval process with the Food and Drug Administration could get its ThermoDox biotechnology on the market in a year or so, Griffin’s analysts say sales won’t begin until 2014 (hitting around $30 million). Griffin’s analysts see sales rising to nearly $400 million by 2017. On the profit front, Griffin sees earnings per share hitting roughly $1.50 by 2016 and $2.50 by 2017.

• It’s important to stress the fluid nature of such forecasts. We still don’t know key variables such as the final share count, eventual marketing partnerships, and of course, whether the FDA even approves ThermoDox.

Which is why it’s important to keep expectations in check, especially for a stock that is quickly becoming a momentum play. As fate would have it, shares have already begun to drift back toward the $4 mark the moment after I purchased shares Monday morning. That’s because some investors that raced into the stock for a quick gain will only stick around until the momentum stops. So this stock could easily be at $3.50 or even $3 before another leg up. I surely hope that’s not the case, but wanted to set proper expectations.

Action to Take — > As this is a fast-moving stock, I intend to provide frequent updates, so please keep an eye out for them. And don’t be shy about taking some money of the table if shares do indeed rise well higher, as I anticipate. No one holding should ever constitute to large a percentage of your portfolio, which can often happen when one stock appreciates sharply.