What is an unusual type of cancer?

Several not in skin: most malignancies are glandular in origin and at least by type can easily be diagnosed. The second most common lesions are of squamous origin. More uncommon are sarcomatous lesions such as extremity epitheliod sarcomas which are rare and deadly, leiomyosarcomas not arising in stomach or uterine fibroid but in vein walls and as Ive just encountered a sarcomatoid carcinoma in the mastoid bone.