This week's 35% jump in the stock of Grail pretty much prices in a positive vote Wednesday, when outside experts meet with the Food and Drug Administration to advise it on approving the first blood test for many kinds of cancer.

With Grail now valued at $4.3 billion, or 19 times the consensus estimate for next year's sales, the stock already seems to be assuming the FDA will approve the test sometime early next year.

Both those outcomes look likely. The advance questions posted Monday by the FDA for its advisors focus on the claims Grail should make in marketing its Galleri test to Americans over 50. The agency didn't question the test's safety and accuracy.

Labs are permitted to sell tests they develop themselves. Grail is already selling Galleri, but the test is rarely covered by insurance. Last year, Grail had sales of about $150 million.

Now the question for investors becomes what kind of sales boost will an approval deliver to Galleri?

Mizuho's Bradley Bowers think the boost will be substantial. He writes Tuesday that sales doubled in the launch years of other cancer-screening products-like colon cancer stool test Cologuard from the Exact Sciences unit of Abbott Laboratories, or the colon cancer blood test Shield from Guardant Health.

Galleri screens a person's blood sample for bits of DNA showing features typical of cancer cells. It tells you if it has found a general signal of cancer somewhere in your body-"Cancer Signal Detected"-and makes its best guess at the kind of tissue where the cancer is hiding.

Clinical trials showed Galleri can detect cancers for which there is no standard screen, such as cancer of the ovary or pancreas. Grail's two big clinical trials showed that it rarely tells you that you have cancer when you don't. When you do have cancer, the test finds it on average about 50% of the 60% of the time.

That is good performance, compared with other widely used screens, like the mammogram. Grail plans to tell customers that they should continue using those standard single-cancer tests, as well.

It's trickier to find definitive proof that tests like Galleri will save lives. The big NHS-Galleri study in Britain failed to prove that screening reduced the number of Stage IV cancers found a year later.

FDA advisors will surely discuss that NHS-Galleri clinical outcome on Wednesday, but it doesn't bear on the safety and accuracy requirements for FDA approval. Most standard screens, like colonoscopies, went into wide use before their lifesaving effectiveness was established in lengthy follow-up trials.

Grail came public two years ago on hopes that DNA blood screens will catch cancer early and allow millions to beat cancers that might have killed or disabled them. Peak annual sales for such tests were forecast at $30 billion to $50 billion.

It has been a slow takeoff. With a $950 price, Galleri sales are expected to reach $180 million this year. Few expect Grail to show a profit in this decade.

The stock has had a big short interest, and a quantitative analysis by UBS concludes that Wall Street's total negative bet against Grail was crowded, compared with the stock's average trading activity. That helps explain the stock's big rise this week, with shorts bailing after seeing the favorable bent of the FDA's posted materials.

Congress passed a law that will require the federal Medicare program to consider covering tests like Galleri, following FDA approval. Most people favor screening tests, but hate paying for them.

So UBS analyst Doug Schenkel estimates that Medicare coverage starting in 2029 will add about $300 million to Grail sales in 2030. Total sales of $1 billion will then be in reach.

At its recent price of $110, Grail has blasted past Schenkel's $105 price target-and that of most Wall Street analysts. Still, events seem to be breaking Grail's way and Schenkel maintains his Buy rating.