Biopsy sample retention mechanism

An apparatus, comprising: a biopsy needle having a distal end and a proximal end, all or a portion of the biopsy needle being movable between a collapsed state and an expanded state; a sheath having a distal end and a proximal end, wherein the biopsy needle in the collapsed state is contained within the sheath, and in the expanded state at least the distal end of the biopsy needle extends from the distal end of the sheath; wherein the biopsy needle is provided with two or more sleeves, which at least partially overlap in the collapsed configuration and which cylindrically expand to provide an increased radius, relative to a radius in the collapsed state, for sampling in the expanded configuration, and wherein a cross section of the distal end of the biopsy needle in the expanded state is a substantially circular cross section.