It was both. The 400+K wasn't one giant monolithic block. It looked like a flurry of large block buys and sells all within the span of a couple minutes. It appears the sells outnumbered the buys and that resulted in the drop from $2.70 to $2.63.
What that fully means or portends I can't say. But clearly the PPS action in ADXS is still weak.
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