This week, the ratings of seven biotechnology stocks on Portfolio Grader are down. Each of these rates a “D” (“sell”) or “F” overall (“strong sell”).

This week, Genomic Health, Inc. (GHDX) falls to a D (“sell”), worse than last week’s grade of C (“hold”). Genomic Health is a life science company, which is focused on the development and commercialization of genomic-based clinical diagnostic tests for cancer that allow physicians and patients to make individualized treatment decisions. In Portfolio Grader’s specific subcategory of Earnings Revisions, GHDX also gets an F. To get an in-depth look at GHDX, get Portfolio Grader’s complete analysis of GHDX stock.

The rating of Acorda Therapeutics, Inc. (ACOR) declines this week from a C to a D. Acorda Therapeutics is a commercial stage biopharmaceutical company dedicated to the identification, development and commercialization of novel therapies that improve neurological function in people with multiple sclerosis (MS), spinal cord injury and other disorders of the central nervous system. The stock gets F’s in Earnings Revisions and Sales Growth. For more information, get Portfolio Grader’s complete analysis of ACOR stock.

The rating of Amarin Corporation Plc Sponsored ADR (AMRN) slips from a C to a D. Amarin focuses on developing the treatment for cardiovascular disease in the field of lipid science. The stock receives F’s in Earnings Growth, Earnings Revisions, Equity and Cash Flow. As of Dec. 4, 2013, 18.8% of outstanding Amarin Corporation Plc Sponsored ADR shares were held short. For a full analysis of AMRN stock, visit Portfolio Grader.

Exelixis, Inc.’s (EXEL) rating falls this week to an F (“strong sell”), down from last week’s D (“sell”). Exelixisis a development-stage biotechnology company dedicated to the discovery and development of small-molecule therapeutics for the treatment of cancer and other serious diseases. The stock receives F’s in Earnings Growth, Earnings Momentum and Equity. Margin Growth and Sales Growth also get F’s. As of Dec. 4, 2013, 25.2% of outstanding Exelixis, Inc. shares were held short. To get an in-depth look at EXEL, get Portfolio Grader’s complete analysis of EXEL stock.

Trius Therapeutics, Inc. (TSRX) earns a D this week, falling from last week’s grade of C. Trius Therapeutics is a biopharmaceutical company. The stock gets F’s in Earnings Growth, Earnings Momentum and Equity. Cash Flow and Sales Growth also get F’s. For more information, get Portfolio Grader’s complete analysis of TSRX stock.

This week, Discovery Laboratories, Inc. (DSCO) drops from a C to a D rating. Discovery Laboratories is a biotechnology company focused on developing products for the treatment of respiratory disease. The stock gets F’s in Equity and Cash Flow. For a full analysis of DSCO stock, visit Portfolio Grader.

Slipping from a C to a D rating, Achillion Pharmaceuticals, Inc. (ACHN) takes a hit this week. Achillion focuses on the discovery, development and commercialization of innovative treatments for infectious diseases. The stock also gets an F in Equity. As of Dec. 4, 2013, 18.5% of outstanding Achillion Pharmaceuticals, Inc. shares were held short. For more information, get Portfolio Grader’s complete analysis of ACHN stock.

Louis Navellier’s proprietary Portfolio Grader stock ranking system assesses roughly 5,000 companies every week based on a number of fundamental and quantitative measures. Stocks are given a letter grade based on their results — with A being “strong buy,” and F being “strong sell.” Explore the tool here.