php - Magento custom report - access generated data

I've created a custom report in Magento fine, but need to add a summery of the data at the bottom. How do I access the generated data to create a summery? Thanks. More information...

$gridBlock = $this->getLayout()->getBlock('adminhtml_report.grid');
$collection = $gridBlock->getCollection();
$item = $collection->getItems();
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But the items are empty, foreach on $collection returns empty as well. The data are shown in the grid area.