Cascade remove in OneToMany relation doesn't work

class Structure
{
    // Id and other variables

    /**
     * @var ArrayCollection $employees liste des employés d'une structure
     *
     * @ORM\OneToMany(targetEntity="Uriae\EmployeeBundle\Entity\Employee", mappedBy="structure", cascade={"all"})
     */
    private $employees;
}

class Employee
{
    // Id and other variables

    /**
     * @var integer $structure
     *
     * @ORM\ManyToOne(targetEntity="Uriae\StructureBundle\Entity\Structure",inversedBy="employees")
     */
    private $structure;
}

// Doesn't work
$em->remove($structure);
$em->flush();

// Bad solution but it works
$em->remove($structure);
$em->flush();
foreach ($employee as $employees)
{
    $em->remove($employee);
}
$e->flush();