Papanicolaou stained smear of a clival chordoma, microscopy. Chordomas are cancers formed of cells which resemble those of the notochord (spine) of a developing foetus. Although they can present anywhere within the spine and skull, the majority grow in the sacral region of the spine, corresponding to the lower back. This image shows a Papanicolaou (Pap) stained smear obtained from a needle biopsy of a chordoma in the clivus, a part of the cranium at the base of the skull. William R. Geddie. CC0 1.0 Universal. Source: Wellcome Collection.