Sciency Thoughts: Malignant Osteosarcoma in a 1.7 million-year-old Hominin Metatarsal from Swartkrans Cave, South Africa.

Malignant Cancers are the biggest singe killer of Modern Humans living in industrialized countries and the second commonest death in developing countries. Many cases of cancer are linked to behaviour or environmental conditions unlikely to have affected our remote ancestors, such as drinking, smoking, obesity or exposure to industrial chemicals or pesticides, and for this reason cancers are often seen as a modern problem, not one that would have affected earlier Human and Hominin populations. However cancers are known in a variety of other higher vertebrates (and, curiously, Hagfish), and are well known of not common in the fossil record, with the earliest known example in a Carboniferous Fish, as well as several cases from Dinosaurs, two from Pleistocene Mammoths, and two instances from Pleistocene Hominins; a 1.98 million-year-old juvenile specimen of Australopithecus sediba from Malapa in South Africa with a spinal lesson attributed to benign osteoid osteoma, and a 120 000-year-old Neanderthal rib from Krapina in Poland showing what appears to be a case of fibrous dysplasia.

In a paper published in the South African Journal of Science on 28 July 2016, a team of scientists led by Edward Odes of the School ofAnatomical Sciences and Evolutionary Studies Institute at the University of the Witwatersrand describe a Hominin metatarsal from Swartkrans Cave in Gauteng State, South Africa (part of the Maropeng Cradle of Humankind World Heritage Site).

The bone was first inspected by Ryan Franklin of Archaeological and Historical Conservancy as part of an unpublished PhD study. It is a Hominin fifth metatarsal with a distinct hemispherical bony mass located on its proximo-ventral end (i.e. the underside of the foot at the end of the bone closest to the leg) dated to about 1.7 million years ago, though it cannot be assigned to a species as the site is known to produce bones of both Homo ergaster and Paranthropus robustus, species which could not be differentiated in an isolated metatarsal even were it healthy. Based upon the visible pathology of the bone, Franklin diagnosed a possible osteoid osteoma (a usually benign form of cancer, forming isolated tumours in bone tissue but not usually spreading), though a full diagnosis was not possible without damage to the specimen.

Hominin 5th metatarsal, exhibiting a hemi-spherical bony mass located on the proximo-ventral aspect of the shaft, abutting the cortical bone surface. P, proximal; D, distal; V, ventral. Odes et al. (2016).

Odes et al. we-examined the specimen using micro-focus X-ray computed tomography at the South African Nuclear Centre for Radiography and Tomography. This enabled the formation of a three dimensional computer model of the specimen, showing its internal structure. The tumour is shown not to be fully fused with the cortex of the bone, but rather to adhere to its surface. It has an irregular spongey texture, with a cauliflower-like appearance. The bone beneath this is covered by a thin layer of new bone with a granular texture and numerous small lessons. The medullary cavity of the bone is largely infilled by new bone growth.

Such a pattern is typical of malignant osteosarcoma, a rapidly developing form of bone cancer that is most commonly found in fast growing areas of the long limb bones, but which is occasionally seen in the metatarsals.

The precise course of maligant cancers can be hard to determine even in living Humans,so determining a precise cause of a cancer in a Middle Pleistocene individual is likely to be impossible. Cancers are often thought of as being modern diseases, brought about by lifestype choices or environmental factors beyond the experience of our earlier ancestors. However some environmental factors associated with cancer today were available in the Pleistocene, such as the radiation in sunlight or radioactive material in granitic rocks. Cancers have also been linked to a number of viral infections, including Human Papilloma Virus, Hepatitis B and C Viruses, Epstein-Barr Virus and Human Immunodeficiency Virus. It is also quite possible that the cancer could have been caused by some interplay of genetics, environment and infection no longer present in Modern Human populations.

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Tuesday, 2 August 2016

Malignant Osteosarcoma in a 1.7 million-year-old Hominin Metatarsal from Swartkrans Cave, South Africa.