Thank you for your question. Generally, there will be a negative reaction to news of a proposed primary offering (the company issues additional shares) or secondary offering (one or more large shareholders are selling their position). A proposed offering is not telegraphed to the market with any real advance notice. As a result, the market is caught by surprise, which often provokes immediate selling of the stock by holders.
If it is a high relative-strength issue, the selling may be limited, as large investors (institutions) who are building positions use the weakness to scoop up shares and add to their holding. Other than this, I am unaware of any historical precedent, as I have not studied offerings and their effect on the market.