INADEQUACY OF APUD CONCEPT IN EXPLAINING PRODUCTION OF PEPTIDE HORMONES BY TUMOURS

118 The working party thanks the Department of Health and Social Security for financial support; the clinicians and other members of staff in the participating centres for their cooperation, and the research assistants for their diligence.

Correspondence should be addressed to Prof. C. J. Roberts, Department of Epidemiology and Community Medicine, Welsh National School of Medicine,

Heath

Park, Cardiff CF4 4XW. REFERENCES

1. 2. 3.

The

Bell RS, Loop JW. utility and futility of radiographic skull examinations for trauma. N Engl J Med 1971; 284: 236-39. Evans KT. The radiologist’s dilemma. Br J Radiol 1977; 50: 299-301. Eyes B, Evans AF. Post-traumatic skull radiographs: time for reappraisal. Lancet 1978; ii: 85-86.

4. Boulis ZF, Dick R. Head

injuries m children-aetiology, symptoms, physical findings and X-ray wastage. Br J Radiol 1978; 51: 851-54. 5. Phillips LA. Emergency services utilisation of skull radiography. Neurosurgery 1979; 4: 580-82. 6. Masters SJ. Evaluations of head trauma:

efficacy of skull films. Am J Neuroradiol 1980;

1: 329-37.

Dogma Disputed INADEQUACY OF APUD CONCEPT IN EXPLAINING PRODUCTION OF PEPTIDE HORMONES BY TUMOURS GEORGE E. MOORE RONALD E. STEVENS Denver General Hospital, Denver, Colorado, Department of Surgery,

7. A national study by the Royal College of Radiologists. A study of the utilisation of skull radiography in 9 accident-and-emergency units in the U.K. Lancet 1980; ii:

1234-37. 8. A national study by the Royal College of Radiologists. Costs and benefits of skull radiography for head injury. Lancet 1981; ii: 791-95. 9. Jennett B. Skull X-rays after recent head injury. Clin Radiol 1980; 31: 463-69. 10. Galbraith S, MacMillan R, Jennett B. X-rays for skull fractures. Lancet 1981; i: 272. 11. Phillips LA. Comparative evaluation of the effect of ahigh yield criteria list upon skull radiography. J Am Coll Emerg Phys 1979; 8: 106-09. 12. Reynolds AF. Letter to the editor. Neurosurgery 1979; 4 (2): 200. 13. Jergens ME, Morgan MT, McElroy CE. Selective use of radiography of the skull and cervical spine. West J Med 1977; 127: 1-4. 14. Lawaetz O. Radiographic investigation of the cranium in emergency investigation of head injuries in a casualty department. Ugeskrift For Laeger 1975; 137: 547-50. 15. Cummins RO, LoGerfo JP, Inui TS, Weiss NS. High-yield referral criteria for post traumatic skull roentgenology. JAMA 1980; 244: 673-76. 16. DeSmet AA, Fryback DG, Thornbury JR. A second look at the utility of skull radiographic examination for trauma. Am J Roentgenol 1979; 132: 95-97. 17. Webber RL, Folio J. Radiographic detectability of occipital and temporoparietal fractures induced in cadaver heads. J Trauma 1976; 16: 115-24. 18. Roberts CJ. Medical care as a risk avoidance procedure: Underwriting the cost of care in the U.K. Br Med J 1982; 285: 751, 754-55.

with ectopic peptide hormone production are automatically "APUDomas" and therefore derived from neuroectoderm. Beyond the controversy over the embryonic origins of normal APUD cells, we believe that it is quite erroneous to use the theory, to explain the behaviour and derivation of malignant cells. There is abundant evidence that cancer cells are able to synthesise a variety of products regardless of their embryological classification.

U.S.A.

REVIEW OF EVIDENCE

The amine precursor uptake and decarbSummary oxylation (APUD) system of cells has been claimed to derive from the embryological neural crest. This assertion has been uncritically accepted. There is much contradictory evidence, especially about the origin of the gastrointestinal and respiratory APUD cells. There is further evidence that the embryological derivation of a particular cell does not relate to the possibility of ectopic peptide hormone synthesis by malignant tumours arising from that cell type. There are many reports of APUD activity by endodermally and mesodermally derived tumours, and of "APUDomas" with endodermal microscopic features. It seems that the concept of dedifferentiation explains the observed data much more satisfactorily and that the presence of double minute chromosomes may denote gene amplification and cellular

The existence of a diffuse endocrine system was first proposed by Friedrich Feyrter in 1938.1 He postulated that the argyrophilic clear cells of the intestine and pancreas (helle Zellen) arose from the surrounding epithelium (endothelium) and had endocrine or paracrine properties. Their existence in the pancreas was explained by a process of local migration or budding (andophytie). In 1955, Pages (at the University ofMontpelier) proposed that these cells had an ectodermal or maybe even a neural crest origin. In the 1960s Pearse et al. linked the peptide-hormone-producing cells together by their similar cytochemical characteristics, and in 1968 proposed the APUD system. Pearse later decided that these endocrine cells were of ectodermal, and specifically of neural crest, origin. The initial list of APUD cells was continually lengthening, and the origin of the new additions was identified as the neural crest, frequently upon ultrastructural or cytochemical grounds. Soon, nearly every peptide-secreting cell in every organ system was allegedly a derivative of the neural crest. Much information, however, had to be ignored or modified in order to consolidate all cells with "nervous" or "endocrine" functions into a unified neuroendocrine controlling system of ectodermal origin. It was not long before controversy erupted over the alleged derivation of these diverse normal and malignant cells with APUD characteristics. Pictet et al., in 1975, excised the entire ectoderm of embryonic rats before the formation of the neural crest, and found normal levels of insulin and normal (3-cells in every pancreas.2 Pearse had earlier inferred the neural crest derivation of the endocrine cells of the gastrointestinal tract and pancreas by indirect means, using formaldehyde-induced fluorescence after levodopa administration to trace the movement of cells from the

production of peptides. INTRODUCTION -

A DIFFUSE system of endocrine cells characterised by certain cytochemical capabilities has been termed APUD (amine precursor uptake and decarboxylation). The peptide hormones they secrete exert powerful control over adjacent cells and distant organs, and it makes a great deal of instinctive "sense" to believe that this system may be closely associated with the central and peripheral nervous systems, and even have a common embryological origin. However, there has been widespread uncritical acceptance of this theory, especially in its expanded forms, and its precepts are ingrained into every medical student as established fact. The little criticism that does exist is centred on the solitary origin claimed for all APUD cells in the neural crest-later modified to include the "neuroendocrine-programmed epiblast". Many cell groups that had long been considered endodermal in derivation were ascribed neuroectodermal origin to fit the theory. We suggest that this reclassification may sometimes result from wishful thinking and be at odds with experimental data. Our objection to the expanded theory centres on the

pervasive misconception that neoplastic processes associated

neural

into the gastric and duodenal primordia, the dorsal pancreas, and elsewhere.3 The migration of neural crest cells into the gastrointestinal and respiratory epithelium was claimed to establish the neuroectodermal origin of the gastrointestinal and respiratory APUD cells. A less presumptive explanation might be that these cells represented neuroblastic precursors of the intramural autonomic ganglion cells. LeDouarin et al. have used the model of quail-chick chimaeras, implanting xenografts from Coturnix coturnix japonica to replace the neural crest of the chicken embryo Gallus gallus.4,5 The migration of the distinctive quail cells was followed and the origin of various structures more directly determined. A conclusion of this study was that the APUD cells of the gastrointestinal tract are endodermally derived, and that the neuroectoderm is not implicated. Epigenic crest

presumptive

119 modification would be one explanation of the presence of the enterochromaffin cells in endodermally derived tissue. Sidhu,in 1979, reviewed the ultrastructural features oftumours more widely agreed to be of neural crest origin, such as medullary carcinoma of the thyroid, carotid body tumours, phaeochromocytoma, and melanoma. He found them to differ from smallcell carcinoma of the lung and carcinoid tumours of the bronchus, appendix, and kidney. Areas of partial squamous differentiation, gland formation, and mucin production in the latter group were felt to be an expression of endodermal rather than neural crest characteristics. Bosman and Louwerens recently examined mature teratomas in an effort to determine the relation of intestinal and respiratory APUD cells to ectodermal derivatives. They found that cells of accepted neural crest origin, such as melanocytes, occurred mostly together with brain tissue, whereas the intestinal and respiratory APUD cell types were almost exclusively found without coexistent brain tissue. They concluded that the evidence was against the ectodermal origin of these APUD cells. Pearse responded by altering his theory of origin,8 claiming that APUD cells not actually derived from the neural crest were at least derived from "neuroendocrine-programmed embryonic ectoblast", or from "neuroendocrine-programmed" cells of placodal or specialised ectodermal origin. However, the literature abounds with reports of peptide hormone production by malignancies not of ectodermal origin. Recently, a case was reported of ectopic ACTH production in a patient with acute myeloblastic leukaemia. The leukaemic marrow cells continued to produce peptide in vitro, a case of APUD characteristics in mesodermally derived patient with a fibrosarcoma, hypoglycaemia, and a high serum insulin level was reported on in 1962-another mesodermal derivative with APUD capability.l° A renal adenocarcinoma producing insulin and glucagon in massive amounts, causing marked fluctuations in the patient’s serum glucose concentration, has been reported. 11 Immunoreactive insulin and glucagon were identified and measured in the tumour. Squamous carcinoma of the cervix has also been shown to produce quantities of insulin sufficient to cause hypoglycaemia. 12 We described a cell line derived from a squamous carcinoma arising from a burn scar that produced parathyroid hormone and carcinoembryonic antigen. 13 There have been several reports of mammary ductal adenocarcinomas producing ectopic parathyroid hormonel4-16 and ACTH.17 Calcitonin production has been linked to poorly differentiated follicular carcinoma of the thyroid, with raised plasma levels measured by radioimmunoassay and localisation to

clear A cells.

cells by immunofluorescence. 18 Tumours with evidence of concomitant APUD and endodermal features have been reported. Dual differentiation of a small cell carcinoma of the lung in squamous and APUD directions has been seen, with bundles of tonofibrils accompanying heurosecretory granules.19 Pancreatic neoplasms incorporating features of both ducts and islets, with some cells containing neurosecretory granules, have also been reported,20,21 as has small cell carcinoma of the oesophagus with souamoid and oat cell features. 22 tumour

DISCUSSION

There are large numbers both of neoplasms with endodermal or mesodermal origins and APUD characteristics, and of "APUDomas" with endodermal ultrastructural features. While certain APUD cells (thyroid C, carotid body, sympathetic ganglia, adrenal medullary, and melanoblast) might normally be derivatives of the embryonic neural ectoderm, many are not. The concept of the "neuroendocrine-programmed ectoblast" seems too diffuse and will likely be very difficult to study. The theory of a separate class of cells to produce most of the peptide hormones and the hypothesis of their neuroectodermal origin is inadequate to explain the behaviour of these malignant tumours in man. We believe that the process ofdedifferentiation unifies the spectrum of ectopic peptide hormone production. Our thesis is that malignant forms of almost all cells are not only structurally more primitive than the normal but may also be

functionally fixed at a level of differentiation where random gene sequences may be activated, leading to the production of various cell products, such as oncofetal proteins or peptide hormones. The aneupolyploid chromosomal complement of malignant cells may contain most of the normal genetic information and multiple copies of some genes. There is no obvious reason why a cell could not produce any substance that is coded into the DNA structure, given the proper conditions of control, or lack of it. Frequently, many double minute chromosomes or "DMs" are detected on karyotyping of malignant tumours. We have established a cell line, COLO 320DM, from a patient with colonic carcinoma which exhibits myriad DMs.23 It appears that there is much gene amplification underway in these cells, since the minute chromosomes seem to be duplicates. The coding sequence has not yet been established. The cells synthesise noradrenline, adrenaline, serotonin, corticotropin, and parathyroid hormone. It seems now that the production of peptide hormones is not even the sole province of eukaryotes. The most basic prokaryotes have now been shown to produce insulin and other peptides. 24 Perhaps our most basic concepts of endocrinology will have to be rethought. All

correspondence should be

addressed

to

G. E. M.

REFERENCES 1. Feyrter F. Ueber diffuse endokrine epitheliale Organe. Zbl Inn Med 1938; 545: 31-41. 2. Pictet RL, Rall LB, Phelps P, et al. The neural crest and the origin of the insulinproducing and other gastrointestinal hormone-producing cells. Science 1976; 191: 191-92. 3. Pearse AGE, Polak JM. Neural crest origin of the endocrine polypeptide (APUD) cells of the gastrointestinal tract and pancreas. Gut 1971; 12: 783-88. 4. LeDouarin NM, Teillet MA. The migration of neural crest cells to the wall of the digestive tract in avian embryo. J Embryol Exp Morphol 1973; 30: 31-48. 5. Fontaine J, LeDouarin NM. Analysis of endoderm formation in the avian blastoderm by the use of quail-chick chimaeras. The problem of the neuroectodermal origin of the cells of the APUD series. J Embryol Exp Morphol 1977; 41: 209-22. 6. Sidhu GS. The endodermal origin of digestive and respiratory tract APUD cells. Histopathologic evidence and a review of the literature. Am J Pathol 1979; 96: 5-15. 7. Bosman FT, Louwerens JWT. APUD cells in teratomas. Am J Pathol 1981; 104: 174-80. 8. Pearse AGE. The diffuse endocrine system and the implications of the APUD concept. Int Surg 1979; 64: 5-7. 9. Pflueger KH, Gramse M, Gropp C, et al. Ectopic ACTH production with autoantibody formation in a patient with acute myeloblastic leukemia. N Engl J Med 1981; 305: 1632-36. 10. Olesky S, Bailey I, Samols E, et al. A fibrosarcoma with hypoglycemia and high seruminsulin level. Lancet 1962; i: 378-80. 11. Pavelic K, Popovic M. Insulin and glucagon secretion by renal adenocarcinoma. Cancer 1981; 48: 98-100. 12. Kiang DT, Bauer GE, Kennedy BJ. Immunoassayable insulin in carcinoma of the cervix associated with hypoglycemia. Cancer 1972; 31: 801-04. 13. Morgan RT, Quinn LA, Woods LK, Moore GE. Marker properties of tumor and lymphoid cell lines derived from a patient with squamous cell carcinoma. Cancer Res 1977; 37: 2030-35. 14. Mavlight GM, Cohen JL, Sherwood LM. Ectopic production of parathyroid hormone by carcinoma of the breast N Engl J Med 1971; 285: 154-56. 15. Hirshorn JE, Vrhovsek E, Posen S. Carcinoma of the breast associated with hypercalcemia and the presence of parathyroid-like substances in the tumor. J Clin Endocrinol Metab 1979; 48: 217-21. 16. Hickey RC, Samaan NA, Jackson GL. Hypercalcemia in patients with breast cancer. Osseous metastases, hyperplastic parathyroid tissue, or pseudohyperparathyroidism? Arch Surg 1981; 116: 545-52 17. Woodard BH, Eisenbarth G, Wallace NR, et al. Adrenocorticotropin production by a mammary carcinoma. Cancer 1981; 47: 1823-27. 18. Calmettes C, Caillou B, Moukhtar MS, Milhaud G, Gerard-Marchant R. Calcitonin and carcinoembryonic antigen in poorly differentiated follicular carcinoma. Cancer 1982; 49: 2342-48. 19. Saba SR, Azar HA, Richman AV, et al. Dual differentiation in small cell carcinoma (oat cell carcinoma) of the lung. Ultrastr Pathol 1981; 2: 131-38. 20. Reid JD, Yuh SL, Petrelli M, et al. Ductoinsular tumors of the pancreas: A light, electron microscopic and immunohistochemical study. Cancer 1982; 49: 908-15. 21. Schlosnagle DC, Campbell WG. The papillary and solid neoplasm of the pancreas: A report of two cases with electron microscopy, one containing neurosecretory granules. Cancer 1981; 47: 2603-10. 22. Reid HAS, Richardson WW, Corrin B. Oat cell carcinoma of the esophagus. Cancer 1980; 45: 2342-47. 23. Quinn LA, Moore GE, Morgan RT, Woods LK. Cell lines from human colon carcinoma with unusual cell products, double minutes, and homogeneous staining regions. Cancer Res 1979; 39: 4914-24. 24. Kolata G. New theory of hormones proposed. Science 1982; 215: 1383-84.