November got off to a bad start for several health-care stocks. Here are three of the worst performers over the past week.

Dialysis paralysis
NxStage Medical (NXTM) ranks as the most horrendous health-care stock this week. Shares plunged more than 22% after the maker of dialysis products announced its third-quarter results.

The top line didn't look bad for NxStage, with revenue hitting a record-high $66.9 million. That figure reflected a 9% jump over the $61.2 million reported in the third quarter of 2012. Earnings, however, were a definite problem. NxStage recorded a loss of $0.08 per share -- worse than the $0.07-per-share loss that analysts surveyed by Thomson Reuters expected.

NxStage's disappointing news didn't stop there. The company lowered its full-year guidance for 2013. Revenue is now expected to be in a range between $261.0 and $262.5 million, compared to previous guidance of $265 to $270 million. NxStage projects a net loss for 2013 in the range of $19.5 to $18.5 million. The company previously forecast a net loss of $17 to $13 million.

Stop drop
Immunogen (IMGN) announced on Tuesday that it was halting a mid-stage study of experimental small-cell lung cancer drug IMGN901. The stop led to a drop in the company's stock of more than 16% for the week.

The problem with IMGN901 was simply that the drug wasn't working well enough to justify continuation of the clinical study. This study compared patients taking Immunogen's drug in combination with etoposide/carboplatin with other patients taking only etoposide/carboplatin. Early data showed that it was unlikely that progression-free survival rates would improve sufficiently to move forward with the study.

This news took such a big toll on Immunogen's stock because IMGN901 was the drug farthest along in the company's internal pipeline. Immunogen does have other drugs in late-stage and mid-stage trials, but all are part of collaborative relationships with other companies.

Hard-to-call fall
Shares of Repros Therapeutics (NASDAQ: RPRX) fell 15% this week. There were a couple of new developments for the company over the past few days, but neither seemed to directly cause the decline.

On Monday, Repros announced that it had received FDA guidance on endpoints for a clinical study of Proellix in treating uterine fibroids. The FDA told the company that it could request that a full clinical hold on the drug be lifted when it submits a new protocol. The stock didn't budge much after this announcement, though.

On Thursday, Repros reported its third-quarter financial results. The earnings numbers weren't great -- Repros lost $0.26 per share. However, that still beat the average analysts' estimate of a $0.32 per share loss. Regardless, most of the stock's drop for the week occurred before the results were announced but after the FDA guidance news.

Bouncing back
I suspect that any of this week's horrendous health-care stocks could bounce back over time. All three have potential despite having a bad few days.

NxStage Medical and Immunogen, in particular, could be stocks to keep on your watch list. At this point, though, waiting and watching seems to be a more prudent course of action than trying to buy on this week's pullbacks.