Are malignant breast lumps usually movable?

Yes. While the "classic" description of a breast cancer is "fixed" and "immovable", I have found many palpable breast cancers to be movable within the breast. The bottom line is that when a woman finds a new lump in her breast, she should seek out medical attention for further evaluation regardless of its mobility within the breast.
Early on. As they grow they may attach to more tissue, muscle, or chest wall, making them more difficult to remove !