NEW YORK (TheStreet) -- The biotech and health care sectors saw big declines last week, raising troubling questions about what's going to happen to the broader stock market in coming sessions.

The one sector that saw a dramatic turn south last week was biotech stocks. The iShares NASDAQ Biotechnology Index (IBB) - Get iShares NASDAQ Biotechnology ETF Report , an exchange-traded fund that tracks the sector, fell a whopping 13% last week.

Typically, we do not see a single sector down more than 10% in a single week, so this was a striking move. Many biotech stocks are listed on the Nasdaq, and that major index was down close to 3% last week. The Russell 2000, a haven for small-cap biotech names, closed down 3.49% for the week.

Take a look at the weekly chart of the iShares NASDAQ Biotechnology Index:

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Chart composed by The Informed Trader, courtesy of Stockcharts

Volume on the 13% move lower was the highest we've seen in a weekly candle going back two and a half years. A key support level comes in near the $285 area and is something to keep tabs on this week.

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Now let's turn our focus to pharmaceutical stocks, which also came under pressure last week. The Market Vectors Pharmaceutical ETF (PPH) - Get VanEck Vectors Pharmaceutical ETF Report fell 6.25% after breaking down through a 4-year rising support line last month.

Here's the weekly chart of this ETF:

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Chart composed by The Informed Trader, courtesy of Stockcharts

Both of these groups have been leaders during the course of our the six-and-a-half-year bull market, but both look to be undergoing significant corrective moves currently if not something worse. And this raises questions about what sectors will provide leadership for the broad market.

After the Federal Reserve meeting this month we saw the banks, industrial stocks and transports come under heavy pressure. The key level looking forward on the S&P 500 index comes in at 1825-1875, which is our rising support line off the 2009 lows as referenced in this article.

This article is commentary by an independent contributor. At the time of publication, the author held no positions in the stocks mentioned.