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Although most skin tumors encountered in veterinary patients are benign, malignant tumor types do occur. Because many are erythematous and pruritic, they can be easily confused with commonly diagnosed pruritic conditions (eg, scabies, allergic disease). The following tumors are commonly misdiagnosed based on their gross appearance. 虽然动物诊所中大多数皮肤肿瘤都是良性的，但是也确实可能会出现恶性肿瘤。因为很多皮肤肿瘤表现为发红瘙痒，很容易就会误诊为瘙痒性疾病（例如疥螨、过敏性疾病）。以下肿瘤根据它们的外观经常会被误诊。
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FIGURE 1 Nodular sebaceous hyperplasia 皮脂腺结节状增生
Benign sebaceous gland tumor on the lateral thorax of a dog. Sebaceous gland tumors develop anywhere sebaceous glands are present, but occur primarily on the limbs and trunk; they can cause discomfort if they become secondarily infected. Sebaceous gland tumors are often observed on canine skin and infrequently on feline skin. These tumors have a recognizable wart-like appearance, but unlike papillomatous skin lesions, do not have a known viral cause. Although most sebaceous gland tumors are classified as the nodular sebaceous hyperplasia type, other types of sebaceous gland tumors—including sebaceous epithelioma, sebaceous adenoma, and sebaceous adenocarcinoma—are differentiated by distinctive histologic features. 犬胸侧壁上的良性皮脂腺肿瘤。任何有皮脂腺的地方都可能长皮脂腺肿瘤，但是主要出现在四肢和躯干；如果继发感染可能会引起不适。犬皮肤上经常发现皮脂腺肿瘤，猫皮肤不常见。这样肿瘤呈疣状，但是跟乳头状瘤样皮肤病变不一样，没有已知的病毒原因。虽然大多数的皮脂腺肿瘤分类为皮脂腺结节状增生，其他类型的皮脂腺肿瘤，包括皮脂腺上皮瘤、皮脂腺腺瘤和皮脂腺腺癌，要通过组织学特点鉴定。
FIGURE 2 Cutaneous papilloma, ventral surface of tail 皮肤乳头状瘤，尾巴腹侧
Solitary, raised, keratinized mass on the tail of a dog. This papilloma has an irregular fronded appearance and a whitish gray-to-yellowish color. Its location (the underside of the tail of a long-haired dog) is considered unusual for development of a cutaneous papilloma, which are more frequently encountered on the head or limbs of dogs. Because of its similarity in clinical appearance to other neoplastic skin lesions, particularly squamous cell carcinoma (SCC), this lesion was surgically removed and submitted for histopathology for definitive diagnosis. 犬尾巴上的单个凸起角质化肿块。这个乳头状瘤从前面看形状不规则，呈白灰到黄色。位置（长毛犬尾巴腹侧）不是皮肤乳头状瘤的常见部位，乳头状瘤更常见于犬头部或四肢。因为外观与其他肿瘤性皮肤病变非常相似，尤其是鳞状细胞癌（SCC），手术切除该病变，送检组织病理学进行确诊。
FIGURE 3 Canine oral papilloma 犬口腔乳头状瘤
Grayish, shiny, solitary pedunculated mass originating from the lip margin of a young dog. Note the classic cauliflower appearance of this mass caused by a papillomavirus as compared with the appearance of the tail mass shown in Figure 2. This benign skin tumor occurs frequently in young (ie, <2 years of age) dogs and usually spontaneously regresses within a few months. Surgical excision may be necessary if multiple masses are present. If lesions become ulcerated, surgical removal and histopathology should be considered to prevent transformation into SCCs. While considered uncommon, progression of papilloma to SCC can occur and has been previously reported.1 一只年轻犬嘴唇边缘灰兮兮发亮的单个带蒂肿块。注意肿块典型的菜花样外观，由乳头状瘤病毒引起，可以与图2 中的尾巴肿块外观进行对比。这一良性的皮肤肿瘤常见于年轻犬（<2岁），通常在几个月内自行消退。如果存在多个肿块，可能需要手术切除。如果病变出现溃疡，应考虑手术切除和组织病理学检查，以免转变成鳞状细胞癌（SCC）。虽然不常见，但是乳头状瘤可能会发展成SCC，并且已有这样的报道。
FIGURE 4 Interdigital cyst 趾间囊肿
Dorsal (A) and plantar (B) appearance of a large keratinized interdigital cyst on the foot of a boxer. Especially important for successful treatment is recognizing that the problematic cyst is located interdigitally on the plantar surface of the foot, whereas the connecting draining tract and much of the observable inflammation and subsequent discomfort is present on the dorsal aspect. Treating the draining tract without addressing the primary problem by completely removing the cyst from the plantar aspect of the foot could result in recurrence of clinical signs. 一只拳狮犬的一个大角质化趾间囊肿足背侧（A）和底侧（B）照片。成功治疗的关键是认识到造成问题的囊肿位于足底侧趾间，而引流窦道和可见的炎症以及随后的不适位于足背侧。如果只治疗背侧的窦道，而不完全切除足底侧的囊肿，会导致临床症状复发。 
FIGURE 5 Feline squamous cell carcinoma in situ, Bowen disease 猫原位鳞状细胞癌，鲍温病
SCC in situ in a cat. SCCs are malignant cutaneous neoplasms routinely diagnosed in dogs and cats. Lightly pigmented dogs and cats can develop neoplastic skin lesions resulting from ultraviolet light exposure. However, SCCs in situ (ie, Bowen disease) are less common in cats and develop regardless of ultraviolet light exposure. Note that this lesion, located above the left eye, is plaque-like and pigmented, which is atypical of SCC neoplasms. Lesions consistent with those of Bowen disease are multiple in number and frequently located on the head but can also be located on the skin of the neck, dorsal trunk, and limbs. As lesions progress, they can bleed easily with minimal manipulation. 一只猫的原位SCC。SCC是常见于犬猫的恶性皮肤肿瘤。浅色犬猫可能会因为暴露于紫外线而出现肿瘤性皮肤病变。然而，原位SCC（也就是鲍恩病）在猫中较少见，不管是否暴露于紫外线之下，都可能会出现。注意这个病变，位于左眼上方，呈斑块状且有色素沉着，是非典型性SCC肿瘤。符合鲍恩病的病变数量很多且常见于头部，但是也可能位于颈部、躯干背侧和四肢皮肤。随着病变发展，轻微触碰可能就很容易出血。 
FIGURE 6 Fibrovascular papillomas, multiple (skin tags) 多个纤维血管性乳头状瘤（皮赘）
Benign tumors in a dog. In this patient, multiple skin tags (fibrovascular papillomas) are located on the skin of the sternum and ventral thorax. The tags are more numerous on the sternum and thus are likely associated with chronic friction or pressure. The pedunculated and pigmented appearance may resemble papilloma-induced viral pigmented plaques, which have been reported in pugs and miniature schnauzers. In contrast, fibrovascular papillomas are not associated with papillomavirus infection, despite the nomenclature, and do not cause clinical problems beyond altered cosmetic appearance. 一只犬的良性肿瘤。这只犬种，多个皮赘（纤维血管性乳头状瘤）位于胸骨和胸腹侧皮肤上。胸骨区域更多皮赘，因此可能与长期摩擦或压迫有关。带蒂且色素沉着看起来像导致乳头状瘤的病毒引起的色素性斑块，在巴哥和迷你雪纳瑞中曾有报道。相反，虽然名字相近，但纤维血管性乳头状瘤与乳头瘤病毒感染无关，而且除了影响外观不会导致其他临床问题。 
FIGURE 7 Fibrovascular papilloma, single (skin tag) 单个纤维血管性乳头状瘤（皮赘）
Unusual fibrovascular papilloma in a dog. This skin tag is focal and not located in an area of known friction or trauma. The narrow stalk and solitary nature of the lesion made it easy to remove via CO2 laser excision. There was no evidence of regrowth or development of new lesions 2 years later. 一只犬的不常见纤维血管性乳头状瘤。该皮赘呈局灶性，且不位于已知有摩擦或创伤的部位。茎很窄且单个使得很容易使用CO2激光将其切除。切除2年后没有复发或出现新的病变。 
FIGURE 8 Milia 粟丘疹
Groups of milium cysts (ie, milia) in a dog. These cysts develop when keratin is trapped beneath the skin surface and accumulates into thin-walled cystic structures. Development of milia in dogs is consistent with steroid excess, similar to that associated with spontaneous or iatrogenic hypercortisolemia, and is particularly common after application of topical corticosteroids. In this dog, multiple very large milia are present in a locally extensive area because of repeated application of a potent topical steroid spray. The well demarcated affected area of skin suggests previous application of a product to this location. In addition, note the large dilated comedones and evidence of cutaneous atrophy, as demonstrated by prominent blood vessels and a crepe-paper appearance of the skin. 一只犬的一群粟丘疹囊肿。当角蛋白被困在皮肤内部且聚集在一个薄壁囊样结构内，就会出现这些囊肿。犬粟丘疹因激素过多而导致，与自发性或医源性高皮质醇血症有感，尤其常见于外用激素后。这只犬中，局部大范围区域因为反复使用强效外用激素喷剂而导致多个很大的粟丘疹。病变皮肤区域有明显的边界提示之前该区域使用过药物。此外，注意毛囊扩张非常大的粉刺以及皮肤萎缩的证据，表现为血管明显以及皮肤呈皱纹纸样。
FIGURE 9 Epitheliotropic lymphoma, feline 猫亲上皮性淋巴瘤
Cutaneous lymphoma located along the medial aspect of the left thoracic limb in a cat. These lesions are pruritic and improve with corticosteroid therapy, making them easily mistaken for eosinophilic plaques, which are steroid-responsive pruritic lesions common in cats. Surface cytology of cutaneous lymphoma neoplasms is not predominantly eosinophilic in nature and, therefore, is not consistent with cytology of an eosinophilic plaque. Findings should prompt the clinician to consider other diagnostic differentials and pursue skin biopsy. 一只猫的皮肤淋巴瘤位于左前肢内侧面。这些病变非常瘙痒，使用皮质类固醇后又好转，使得很容易将其误诊为嗜酸性斑块，后者是猫常见的激素反应性瘙痒性病变。皮肤淋巴瘤的皮肤表面细胞学本身主要细胞不是嗜酸性粒细胞，因此不符合嗜酸性斑块。这些发现应促使兽医考虑其他可能的鉴别诊断并进行皮肤活检。
FIGURE 10 Epitheliotropic lymphoma, canine 犬亲上皮性淋巴瘤
Cutaneous lymphoma lesions located in the inguinal region of a dog. Patients with this type of lesion are intensely pruritic, and lesions can be very similar in clinical appearance to lesions caused by staphylococcal pyoderma, demodicosis, or dermatophytosis. Note the erythematous borders of these lesions along with the circular rims of scale along the periphery and varying degrees of hyperpigmentation. These features are similar to a bacterial skin infection secondary to allergic dermatitis. Epitheliotropic lymphoma is more common in dogs more than 10 years of age; however, the pruritus associated with this disease may be steroid-responsive, and progression of the disease is slow, which may complicate diagnosis. 一只犬腹股沟区域的皮肤淋巴瘤。有这种病变的动物强烈瘙痒，且病变可能与葡萄球菌性脓皮症、蠕形螨或皮肤癣菌的病变非常相似。注意这些病变边缘发红以及外周有一圈皮屑，且有不同程度的色素过度沉着。这些特点与继发于过敏性皮炎的细菌性皮肤感染非常相似。亲上皮性淋巴瘤在10岁以上的犬中更常见；然而，该疾病导致的瘙痒可能对激素有反应，并且该病进展得非常慢，继而可能导致诊断复杂化。
FIGURE 11 Mast cell tumor, feline 猫肥大细胞瘤
Cutaneous mast cell tumor (MCT) in a cat. Note the discrete raised masses above both eyes, one of which has surface crust formation. MCTs in cats occur much more commonly on the skin of the head and neck; although discrete masses are more obvious, some patients present with areas of indistinct swelling or lesions that appear more like sebaceous gland tumors when near the eye itself. 一只猫的皮肤肥大细胞瘤（MCT）。注意双眼上方清晰的凸起肿块，其中一个表面有结痂。MCT在猫中更常见于头颈部皮肤；虽然清晰的肿块更明显，但是一些猫可能只是有不明显的肿胀或病变，看起来更像皮脂腺肿瘤，当位于眼睛附近时。
FIGURE 12 Mast cell tumor, canine 犬肥大细胞瘤
Cutaneous MCT in a dog. On initial examination, the MCT on the lateral aspect of the head has a very similar clinical appearance to that of pyotraumatic dermatitis. However, cytology findings were not primarily neutrophilic with intracellular and extracellular cocci, as would be expected with a diagnosis of pyotraumatic dermatitis. Instead, the mast cells were poorly differentiated without granules, making cytologic diagnosis challenging when compared with findings for most canine cutaneous MCTs. 一只犬的皮肤MCT。初诊时，头外侧的这个MCT看起来非常像脓性创伤性皮炎。然而，细胞学发现不是以中性粒细胞和胞内以及胞外球菌为主，这些特点在脓性创伤性皮炎时会出现。相反，细胞学上出现很多分化不良没有颗粒的肥大细胞，与大多数犬皮肤MCT细胞学结果相比，使得细胞学诊断十分困难。
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