Biotech's mid-cap space is a closely watched sector because it serves as a feeder pool for tomorrow's top tier companies. Of the 30 companies that began the year as mid-cap plays - defined by BioCentury as market valuations between $700 million and $3 billion - nine had graduated by the end of the second quarter into the large cap space occupied by companies valued above $3 billion. Some companies made it through organic growth, while others did it by combining stables. The latter group includes Shire (LSE:SHP; SHPGY) through its January merger with Roberts Pharmaceutical, and Celltech (LSE:CCH;CLL), which acquired Medeva and Chiroscience.

The other keys for moving up in the first half were to have reached the market or to be antibody plays. Of the nine, eight have products on the market, while two - Abgenix (ABGX) and Protein Design (PDLI) (which also has a marketed product) - have MAb platforms. Another MAb developer - Medarex (MEDX) - was knocking on the big cap door with a $2.97 billion valuation at June 30.

Other companies on the cusp of the $3 billion threshold were structural drug design play and HIV drug marketer Vertex (VRTX); specialty biological manufacturer and distributor Techne (TECH) and genomics informatics play Incyte (INCY).

Only PowderJect (LSE:PJP) dropped into the lower tier. The developer of needleless technologies to deliver pre-filled dry powers saw its market cap fall to $453.7 million from $980.7 million in the first half after merger rumors with Peptide Therapeutics (LSE:PTE) didn't pan out, and then it posted bigger losses than anticipated for its year ended March 31.