The article does claim that nanomedicines, in this case nanoshells, do accumulate around tumor cells because of leaky blood vessels.
Aaron
When West and her colleagues infused her nanoshells into the bloodstreams of mice with cancer, the spheres traveled through the circulatory system and then concentrated around the animals' tumors -- a fortuitous result of the fact that blood vessels tend to be leaky near tumors. Then the team exposed the animals to the near infrared light. The nanospheres quickly absorbed that energy and heated up to about 122 degrees Fahrenheit, cooking the tumors but leaving surrounding tissues unharmed.
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