Computer Frame No.

Principles of Pathology Autotutorial Laboratory
D.W. Hayden

Alterations of Cell Growth and Multiplication
Nonneoplastic Changes in Cell Growth
( Computer Frames 1- 48 ) Hyperplasia - increase in size of an organ or tissue via an increase in cell numbers Hyperplastic changes are routinely encountered in certain organs of aged animals, especially dogs and cats. Major organs that retain the capacity to replicate tissue subunits are most commonly involved. These include glands (exocrine and endocrine), intestinal mucosa as well as the hematolymphoid tissues (spleen, bone marrow and lymph nodes). In some instances the cause of hyperplasia is unknown while in others hyperplasia can be attributed to altered tissue response to hormones or growth factors. Other important causes of hyperplasia are chronic inflammation, chronic irritation, and exposure to certain chemicals or drugs. Frame No. 1. Nodular pancreatic acinar cell hyperplasia (dog) - Multiple, raised cream-colored foci in a section of pancreas beside the duodenum 2. Nodular pancreatic acinar cell hyperplasia (dog) - Subcapsular hemorrhage is also seen at the angle of the pancreas 3. Nodular pancreatic acinar cell hyperplasia (cat) - Note multifocal cream-colored nodules similar to those seen in the dog pancreas (frames 1&2) 4. Nodular pancreatic acinar cell hyperplasia (cat) - Exocrine cells form solid micronodules in contrast to regular acini. 5. Nodular pancreatic acinar cell hyperplasia (cat) - Compact exocrine cells form a solid nodule with few defined acini and no lobulation 6. Nodular splenic lymphoid hyperplasia (dog) - Note multiple, raised , dark red subcapsular nodules 7. Nodular hepatocellular hyperplasia (dog) - Multiple, flat or raised tan foci in a liver lobe 8. Nodular hepatocellular hyperplasia (dog) - Pale nodules composed of hepatocytes are clearly outlined in formalin-fixed liver sections 9. Nodular hepatocellular hyperplasia (dog) - This cirrhotic (end-stage liver) demonstrates the remarkable regenerative capability of hepatocytes 10. Benign prostatic hyperplasia (dog) - Bilobed prostate has an irregular capsular surface and exceeds the urinary bladder in size; chronic prostatitis was also present 11. Benign prostatic hyperplasia (dog) - The prostate has a relatively smooth contour and exceeds the urinary bladder in size 12. Benign cystic prostatic hyperplasia (dog) - Sectioned surface of the prostate reveals numerous cysts 13. Normal prostate histology (dog) - Columnar epithelial cells with abundant secretory granules line the acini 14. Benign prostatic hyperplasia (dog) - Microscopically, prostatic acini have a pronounced papillary growth pattern (compare to frame 13 ) 15. Benign cystic prostatic hyperplasia (dog) - Dilated acini filled with secretion show some intraacinar epithelial projections (see frame 12 ) Food for Thought What pathological conditions are most often associated with prostatomegaly in the dog? 16. Hepatic coccidiosis (rabbit) - Numerous elongated subcapsular white spots represent markedly dilated hyperplastic bile ducts infected by Eimeria stiedae 17. Hepatic coccidiosis (rabbit) - Dilated bile ducts are lined by proliferated epithelium thrown into many papillary folds 18. Hepatic coccidiosis (rabbit) - Bile duct epithelium is infected with spherical intracellular stages of the parasite. A few elongated oocysts and spherical infective stages are in the duct lumen 19. Mammary gland fibroepithelial hyperplasia (cat) - Extreme mammary development in this 8-month old cat represent an abnormal response to progestin stimulation 20. Mammary gland fibroepithelial hyperplasia (cat) - Discrete, cream-colored subcutaneous masses typify an accentuated degree of lobular hyperplasia [AKA., mammary hypertrophy] (same cat as frame 19) 21. Mammary gland fibroepithelial hyperplasia (cat) - Bilateral, uniformly enlarged subcutaneous masses in a 1-year old cat 22. Mammary gland fibroepithelial hyperplasia (cat) - Note individual mammary masses are divided into smaller subunits called lobules (same cat as frame 21) 23. Mammary gland fibroepithelial hyperplasia (cat) - Both ductular cells and periductular stroma have undergone hyperplasia; proportionally there is much more stroma 24. Mammary gland fibroepithelial hyperplasia (cat) - Note the relatively uniform size and alignment of ductular epithelial cells; myoepithelial cells basally and secretory epithelial cells luminally Food for Thought How would you distinguish feline mammary fibroepithelial hyperplasia from mammary cancer? What is the cause of mammary fibroepithelial hyperplasia in cats ? Hypertrophy - an increase in size of a cell, tissue or organ Although hypertrophy and hyperplasia are by definition separate processes, there are numerous instances where they both occur together. For example, cellular hyperplasia and hypertrophy both contribute to enlargement of the prostate gland. On the other hand, an increase in cardiac muscle mass and an enlarged heart are produced by hypertrophy of cardiac muscle fibers, since the heart retains little proliferative capacity in adults. 25. Hypertrophic cardiomyopathy (cat) - The heart is enlarged and occupies about one-third of the thoracic cavity; grainy surface of the liver is from chronic passive congestion 26. Hypertrophic cardiomyopathy (cat) - The left ventricular free wall and the interventricular septum are markedly thickened. This severely reduces the capacity of the left ventricle chamber 27. Hypertrophic cardiomyopathy (cat) - Cross sections of the heart at several levels shows a progressive increase in thickness of the left ventricular free wall and septum leading to a diminutive ventricular chamber 28. Hypertrophic cardiomyopathy (cat) - Microscopically, cardiac muscle fibers are disorganized, wide and separated by increased interstitial stroma 29. Hypertrophic cardiomyopathy (cat) - A trichrome stain reveals marked variation in cardiac muscle fiber size, dropout of muscle fibers and moderate interstitial fibrosis ( red= muscle, blue= connective tissue ) 30. Dilated cardiomyopathy (cat) - The left ventricle and atrium have markedly dilated chambers ( compare to hypertrophic cardiomyopathy, frame 26 ) Food for Thought What are the three major types of feline cardiomyopathy and how do they differ pathologically In what other domestic animal is cardiomyopathy common ? Atrophy and Hypoplasia - atrophy is an acquired decrease in size of cells, tissues, or organs.. Decreased function causes organs to atrophy. If an organ or tissue is congenitally underdeveloped the proper term is hypoplasia. 31. Serous atrophy of fat (foal) - Gelatinous appearance of fat around coronary vessels is the result of malnutrition 32. Serous atrophy of fat (calf) - Gelatinous appearance of fat in the bone marrow signals a state of advanced malnutrition 33. Exocrine pancreatic atrophy (dog) - Lacy tissue adjacent to the duodenum contains remnant pancreatic lobules, ducts and blood vessels 34. Exocrine pancreatic atrophy (dog) - Microscopically, the pancreas consists of atrophic lobules and large ducts surrounded by adipose tissue. Note the absence of inflammation 35. Unilateral testicular atrophy (dog) - The atrophic testicle has a thickened capsule while the contralateral testis has one red and one cream-colored interstitial cell tumor 36. Unilateral renal atrophy (cat) - The small kidney is about one fifth the mass of the larger kidney. The large kidney reflects compensation (compensatory hypertrophy) for loss of renal function 37. Unilateral renal hypoplasia (dog) - The minuscule kidney is hypoplastic while the other kidney is enlarged to compensate for lost renal function. Pyelonephritis (red and yellow streaks in cortex) is present in the hypertrophied kidney 38. Cerebellar hypoplasia (cat) - Compare normal cerebellum on the left with hypoplastic cerebellum on the right. Cerebellar hypoplasia is caused by an inutero infection with feline panleukopenia virus 39. Cerebellar hypoplasia (calf) - Note small cerebellum caused by inutero infection with bovine virus diarrhea virus Food for Thought Are there differences and similarities between starvation and malnutrition? or are the terms synonymous ! What are some causes of organ atrophy? Metaplasia - a differentiated tissue of one kind is replaced by a differentiated tissue of another kind. Normally, metaplasia is identified as a microscopic change in tissues. Examples include conversion of secretory epithelium to squamous epithelium (squamous metaplasia) or conversion of fibrous connective tissue to bone (osseous metaplasia). 40. Squamous metaplasia of prostate (dog) - Squamous epithelial cells have replaced the normal columnar secretory epithelium. Hyperestrogenism from a testicular sertoli cell tumor is responsible for the change in type of epithelium in this dog (compare to frame 41) 41. Normal prostatic secretory epithelium (dog) - Note intense eosinophilic staining in apical cytoplasm of columnar secretory cells 42. Osseous metaplasia (cat) - Adenocarcinoma from the peritoneal cavity contains metaplastic bone in stroma between neoplastic glands 43. Osseous metaplasia (dog) - Mammary adenocarcinoma with osseous metaplasia in the connective tissue stroma Food for Thought How might metaplasia be viewed as useful to the host in one situation and of no apparent value in another situation? Dysplasia - strictly speaking dysplasia means an abnormality of development.. This term can be applied to gross anatomic defects such as hip dysplasia, or to microscopic alterations of cell growth that are too irregular to by called hyperplasia and not irregular enough to be called cancer (e.g., cervical dysplasia) 44. Renal dysplasia (dog) - Note small kidneys with uneven capsular surface and excessively clefted hilar area (6-week old Cocker Spaniel) 45. Renal dysplasia - Sagitally sectioned surface of kidneys reveals decreased medullary tissue and an irregular pelvic outline (same case as frame 44) 46. Renal dysplasia (dog) - This progressive form of nephropathy features an irregular capsular surface, reduced cortical mass and white areas of fibrosis. Dog was 9 months-old and had been sick for 6 months 47. Mammary gland dysplasia (cat) - Mammary ductule lined by disorganized epithelium. Atypical cell alignment and cells with enlarged and multiple nucleoli are seen 48. Hip dysplasia (dog) - Severe erosion of articular cartilage on the femoral head is accompanied by a thickened coxofemoral joint capsule and proliferation of granulation tissue in the acetabular space Neoplastic Cell Growth ( Computer frames 49-141) Tumors are derived from epithelial or mesenchymal tissues and are designated benign or malignant depending on their gross and microscopic features, and biologic behavior. The four basic types of tissue - epithelial, connective, muscular and nervous - each have their own benign and malignant tumors. Epithelial Tumors - Benign epithelial tumors are called adenomas if derived from glandular epithelium, epitheliomas when originating from skin, polyps or papillomas if projecting from a surface or into a lumen. Name of the organ or tissue should precede the descriptors given above (e.g., adrenal cortical adenoma, sebaceous cell epithelioma, squamous cell papilloma, gastric polyp). Malignant epithelial tumors are called carcinomas. 49. Esophageal squamous papilloma (cow) - Multiple white papillomas with a papilliform surface project from the esophageal mucosa 50. Cutaneous papillomatosis (rabbit) - A cluster of squamous papillomas (warts) decorate the head of this animal. Thick layers of surface keratin harden these lesions resulting in formation of so-called cutaneous horn 51. Squamous papilloma (dog) - Microscopically, squamous epithelial projections covered by keratin are supported by a connective tissue core 52. Squamous papilloma (dog) - Microscopically, the deep border of this benign tumor consists of anastomosing pegs of squamous epithelium accompanied by a moderate infiltrate of mononuclear inflammatory cells ( same case as frame 51 ) 53. Gastric polyps (dog) - Several polyps on long stalks emanate from the gastric mucosa in body of the stomach 54. Pharyngeal squamous cell carcinoma (cat) - A cup-shaped mass with irregularly thickened sides occupies the posterior oropharyngeal region 55. Gastric squamous cell carcinoma (horse) - A fungated mass of necrotic neoplastic tissue occupies the squamous lined part of the stomach 56. Gastric squamous cell carcinoma (horse) - Cross section of the stomach reveals marked thickening of the gastric wall from extensive cancerous infiltration. This process has fused the stomach to the liver ( same case as frame 55 ) 57. Metastatic gastric squamous cell carcinoma (horse) - Extensive peritoneal implantation of squamous cell carcinoma on the surface of the diaphragm (same case as frames 55 & 56 ) 58. Tonsilar squamous cell carcinoma (dog) - Microscopically, the tonsil is effaced by nests, cords and spaces lined by squamous epithelium. Spaces contain keratin and necrotic cell debris. Note fibrosis and the absence organized lymphoid tissue 59. Tonsilar squamous cell carcinoma (dog) - Microscopically, solid nests of squamous epithelial cells show central necrosis and laminated keratin, so-called keratin pearls 60. Tonsilar squamous cell carcinoma (dog) - Microscopically, note abnormal keratinization of a squamous epithelial cell ( dyskeratosis ) 61. Squamous cell carcinoma (dog) - Microscopically, tumor cells are well differentiated and exhibit prominent intercellular bridges ( desmosomes ), a characteristic feature of squamous epithelium 62. Metastatic squamous cell carcinoma (dog) - Microscopically, an island of neoplastic squamous epithelium is embedded in the cortex of this lymph node 63. Metastatic squamous cell carcinoma (dog) - Microscopically, cancerous squamous epithelial cells replace lymphoid tissue in this lymph node ( same case as frame 62 ) 64. Gastric adenocarcinoma (dog) - The mucosa is extensively ulcerated and the gastric wall is thickened 65. Gastric adenocarcinoma (dog) - Note large ulcer in the pyloric antrum surrounded by smaller ulcers; swollen rugae are seen in body of the stomach 66. Gastric adenocarcinoma (dog) - Microscopically, the mucosa and submucosa are diffusely infiltrated by cancerous cells; red band in center is the muscularis mucosa 67. Gastric adenocarcinoma (dog) - Microscopically, hyperchromatic cancerous epithelial cells, individual and grouped, are intermixed with reactive spindle-shaped fibroblasts in the stomach submucosa 68. Metastatic gastric adenocarcinoma (dog) - Microscopically, tumor emboli occupy the subcapsular sinus and have infiltrated the adjacent parenchyma in this regional lymph node 69. Pancreatic acinar cell adenoma (cat) - A discrete raised tumor nodule with an irregular surface projects from the exocrine pancreas 70. Pancreatic acinar cell adenoma (cat) - Microscopically, tumor architecture closely replicates the acini found in normal pancreas ( same case as frame 69 ) 71. Pancreatic adenocarcinoma (cat) - The omentum is thickened and lumpy from infiltration or implantation of cancerous pancreatic acinar cells. The syringe contains an abdominal transudate secondary to the cancer 72. Mammary gland adenocarcinoma (cat) - Multiple tumors, some ulcerated are seen in the abdominal mammary glands 73. Mammary gland adenocarcinoma (cat) - Ulcerated multinodular mass removed from the mammary chain 74. Metastatic mammary gland adenocarcinoma (cat) - The lungs, ventral and posterior mediastinum are virtually replaced by cancerous mammary epithelial cells 75. Metastatic mammary gland adenocarcinoma (cat) - Plaques of cream-colored metastatic cancer tissue cover the intercostal pleura (same case as frame 74 ) 76. Mammary gland adenocarcinoma (cat) - Microscopically, numerous neoplastic acini are separated by collagenous stroma while normal mammary tissue is absent. Male cat given progestins 77. Mammary adenocarcinoma (cat) - Microscopically, branching stromal cores lined by neoplastic epithelial cells project into irregular spaces containing necrotic epithelial cells 78. Malignant melanoma (dog) - Black mass projects from maxillary gingiva in the oral cavity of this animal 79. Malignant melanoma (horse) - Cross sections of the tail, of an old gray horse, show extensive replacement of the coccygeal muscles by heavily pigmented tumor cells 80. Malignant melanoma (dog) - Microscopically, this malignant melanoma consists of sheets of neoplastic cells with and without abundant brown melanin pigment 81. Malignant nasal melanoma (dog) - Needle aspirate reveals some pigmented tumor cells as well as abundant green/black background pigment from ruptured tumor cells (Wright’s stain) 82. Malignant nasal melanoma (dog) - Needle aspirate shows a cluster of tumor cells with fine cytoplasmic granules ( Wright’s stain) 83. Metastatic malignant melanoma (dog) - Metastatic tumor nodules in the kidney and adrenal gland are heavily pigmented 84. Metastatic malignant melanoma (dog) - The multifocal black spots that diffusely involve all lung lobes represent metastatic malignant melanoma while the white foci are metastasis from a mammary gland adenocarcinoma 85, Prostatic adenocarcinoma (dog) - An enlarged smooth contoured prostate gland and distended urinary bladder are the result of prostate cancer in a neutered male dog 86. Prostatic adenocarcinoma (dog) - Cross sections of the prostate gland reveal a lobulated pattern of cream-colored tissue and multifocal areas of necrosis with cavitations ( same case as frame 85) 87. Prostatic adenocarcinoma (dog) - Microscopically, prostatic architecture has been markedly altered by neoplastic polyhedral to spindle-shaped epithelial cells that line and occupy irregularly shaped spaces Mesenchymal tumors - These tumors are derived from tissues of mesenchymal origin (fibrous connective tissue, muscle, bone, bone marrow, blood vessels and lymphatics, nerves and lymphoid tissues). Malignant tumors of connective tissue are called sarcoma, of bone marrow leukemia and of lymphoid tissue lymphoma. Morphologically, mesenchymal tumor cells may be round (leukemia and lymphoma) or spindle-shaped (sarcoma). Specific identification of look alike tumors requires demonstration of special cell products ( e.g., histamine granules in mast cells, immunoglobulins in plasma cells etc.). 88. Fibroma (cow) - Raised white plaque in the esophageal wall 89. Cutaneous fibroma (dog) - A moderately cellular tumor composed of spindle cells aligned in parallel fashion 90. Cutaneous fibroma (dog) - A moderately cellular tumor composed of interlacing bundles of fibroblasts 91. Fibrosarcoma (dog) - White bands of fibrous tissues subdivide this tumor removed from a dog’s neck. Pale yellow tissue represents tumor necrosis 92. Myxofibrosarcoma (cat) - The caudal thigh muscles are heavily infiltrated by cream-colored nodules of neoplastic tissue. Cavitations contained abundant connective tissue mucin 93. Fibrosarcoma (dog) - Note the high degree of cellularity in comparison to a fibroma (see frames 89&90) 94. Fibrosarcoma (dog) - A highly cellular tumor composed of spindle cells with hyperchromatic nuclei, frequent mitoses and scant collagen (compare to frames 89 & 90) 95. Fibrosarcoma (dog) - The cytoplasm of tumor cells are clearly labelled with anti-vimentin, an intermediate filament found in mesenchymal cells 96. Lipoma (dog) - Benign fatty tumor that easily shelled out of the subcutaneous fat 97. Lipoma (dog) - Microscopically, a lipoma is nearly identical in histologic appearance to normal fat ; 11 year-old Doberman 98. Pleomorphic sarcoma (cat) - A large ulcerated mass protruds from the lateral surface of the tibiotarsal joint. Note accessory subcutaneous nodules along the distal tibia 99. Pleomorphic sarcoma (cat) - This multinodular tumor is wrapped around the tibiotarsal joint as viewed caudally (same case as frame 98) 100. Pleomorphic sarcoma (cat) - An impression smear of the tumor reveals a population of pleomorphic cells including some multinucleated tumor giant cells ( same case as frame 98) 101. Pleomorphic sarcoma (cat) - Microscopically, tumor cells in this tissue section closely mirror tumor cells in the impression smear ( same case as frame 98 ) 102. Gastric leiomyoma (dog) - This benign smooth muscle tumor has been incised to show several lobules of well circumscribed white tissue at the cardioesophageal junction 103. Gastric leiomyoma (dog) - Microscopically, the gastric leiomyoma is nonencapsulated and more compact than the surrounding normal smooth muscle fibers 104. Gastric leiomyoma (dog) - Microscopically, smooth muscle cells in a leiomyoma closely mimic bundles of normal smooth muscle seen at the tumor periphery 105. Vaginal leiomyosarcoma (dog) - Microscopically, tumor cells have round to oval nuclei with clumped chromatin, prominent single or multiple nucleoli and mitotic activity ( compare to leiomyoma in frame 104) 106. Vaginal leiomyosarcoma (dog) - Microscopically, tumor cells are readily identified by showing strong immunoreactivity to smooth muscle actin 107. Hemangioma (dog) - Multiple dilated and thick walled benign vascular channels contain blood and a microthrombus 108. Hemangioma (dog) - Thin endothelial cells resting on thick connective tissue septa line spaces filled with blood ( same case as frame 107) 109. Cardiac hemangiosarcoma (dog) - Marked hemopericardium from a ruptured right atrial hemangiosarcoma. Aspirated blood is seen in syringe 110. Cardiac hemangiosarcoma (dog) - A dark red tumor mass bulges from the surface of the right atrium 111. Disseminated hemangiosarcoma (dog) - Many dark red tumor foci are scattered throughout the lungs and the abdominal organs 112. Splenic hemangiosarcoma (dog) - The large circular mass in the abdominal cavity is a splenic hemangiosarcoma covered by omentum 113. Splenic hemangiosarcoma (dog) - Many raised neoplastic nodules with cream-colored areas of necrosis occupy the spleen 114. Hemangiosarcoma (dog) - Hemangiosarcoma involving the spleen, liver and lungs. Spleen is a likely site for the primary tumor 115. Hemangiosarcoma (dog) - Dark circular areas in the liver are presumed to be metastases from the spleen ( same case as frame 114) 116. Cutaneous mast cell tumor (dog) - Subcutaneous nodule on the left rear leg accompanied by marked scrotal swelling. Antiseptic stains the skin orange 117. Cutaneous mast tumor (cat) - Note multiple hairless nodules on the head of this cat 118. Splenic mast cell sarcoma (cat) - Infiltrates of malignant mast cells produced marked splenomegaly and a thickened ( white ) splenic capsule. Note small spleen from a normal cat for comparison 119. Cutaneous mast cell tumor (dog) - Many loosely aggregated neoplastic mast cells have infiltrated between bundles of collagen 120. Cutaneous mast cell tumor (dog) - Round mast cells with clearly defined cell membranes are commingled with eosinophils 121. Cutaneous mast cell tumor (dog) - Stains, like toluidine blue, giemsa, or Wright’s stain are used to demonstrate metachromatic granules in the cytoplasm of mast cells 122. Cutaneous mast cell tumor (dog) - Needle aspirate reveals many well differentiated mast cells with abundant metachromatic staining granules (Wright’s stain) 123. Cutaneous mast cell tumor (dog) - Needle aspirate shows several heavily granulated mast cells and free granules from ruptured cells (Wright’s stain) 124. Metastatic mast cell sarcoma (dog) - Clustered and loosely aggregated mast cells are present in the sinusoids of this lymph node 125. Metastatic mast cell sarcoma (dog) - Toluidine blue stain reveals metachromatic staining of cytoplasmic granules in mast cells within sinusoids of the lymph node (same case as frame 124) 126. Cardiac lymphosarcoma (cow) - Red and yellow nodules composed of malignant lymphoid cells occupy the right atrium 127. Cardiac lymphosarcoma (cow) - Microscopically, diffuse infiltrates of hyperchromatic round cells replace cardiac myocytes 128. Anterior mediastinal lymphosarcoma (cat) - The thymic region is replaced by a multinodular, cream-colored mass of neoplastic lymphoid tissue. Note displacement of thoracic viscera 129. Lymph nodes, lymphosarcoma (dog) - Several greatly enlarged and reddened abdominal lymph nodes surround the post cava near hilus of the liver 130. Lymph node, lymphosarcoma (dog) - Needle aspirate stained with new methylene blue reveals a uniform population of discrete hyperchromatic round cells (malignant lymphocytes) 131. Abomasal lymphosarcoma (cow) - A localized area of the abomasal mucosa is raised and irregularly thickened by infiltration of neoplastic lymphoid cells 132. Abomasal lymphosarcoma (cow) - Cross sections of the abomasum ( top ) an ulcerated abomasal fold ( right ) and a regional lymph node ( left ) show diffuse cream-colored tissue representing a massive infiltrate of neoplastic lymphoid cells 133. Uterine lymphosarcoma (cow) - The uterine mucosa has been exposed to reveal several discoid tanish-white masses composed of neoplastic lymphoid tissue 134. Uterine lymphosarcoma (cow) - Saggital and cross sections of a palpably thickened uterine horn reveal diffuse cream-colored infiltrates of neoplastic lymphoid cells 135. Appendicular osteogenic sarcoma (dog) - The dorsal radiocarpal area in this St. Bernard was firm, swollen and ulcerated 136. Appendicular osteogenic sarcoma (dog) - Saggital section of the radiocarpal joint of a St. Bernard reveals medullary extension of the tumor. There is periosteal production of new bone concomitant with destruction of cortical bone. Classically, the joint space is not involved 137. Appendicular osteogenic sarcoma (dog) - Radiographic appearance of a distal radial osteogenic sarcoma in a St. Bernard. Tumor extension and mineralization, impart a sunburst appearance in the surrounding soft tissues 138. Metastatic osteogenic sarcoma (dog) - Large, firm, white metastatic tumor nodules are seen throughout the lung. The primary tumor was in a rib 139. Metastatic osteogenic sarcoma (dog) - Cut surface of the lung reveals multiple pulmonary metastasis from an osteogenic sarcoma. These foci are firm, white and well delineated. Tumor nodules that produce bone often impart a gritty sensation when incised ( same case as frame 138 ) 140. Osteogenic sarcoma (dog) - Microscopically, some groups of tumor cells are surrounded by abundant eosinophilic deposits of unmineralized bone called osteoid. Other tumor cells show no evidence osteoid production 141. Osteogenic sarcoma (dog) - Seams of eosinophilic osteoid encompass many tumor cells. The presence of osteoid helps to differentiate an osteogenic sarcoma from other types of sarcoma Food for Thought What is the difference between a carcinoma and a sarcoma? This question is commonly asked by senior veterinary students. How can this information be applied to treatment of cancer?