Original Research

Gone Fishing: A Unique Histologic Pattern in Cutaneous Angiosarcoma

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Cutaneous angiosarcoma is a rare but aggressive vascular malignancy that can present a diagnostic challenge due to a wide variety of clinical appearances and histologic features. Final diagnosis traditionally is yielded by corroborating the histologic and immunohistochemical findings with the clinical presentation; however, a histologic feature known as “fish in the creek,” which consists of free-floating or tufted pleomorphic spindle cells within the vascular lumen, may be an additional diagnostic clue. In this study, we aimed to determine the diagnostic utility of this finding in cutaneous angiosarcoma. Our results suggest that “fish in the creek” has the potential to be an additional useful diagnostic tool for an otherwise challenging and deceptive malignancy.

Practice Points

  • The histologic finding of “fish in the creek” is characterized by free-floating or tufted pleomorphic spindle cells within the vascular lumen.
  • Fish in the creek has only been demonstrated in cutaneous angiosarcoma when compared to histologic findings of other similar vascular malignancies.
  • The fish-in-the-creek finding may be an additional diagnostic tool in cases of cutaneous angiosarcoma.



Cutaneous angiosarcoma is a rare malignant tumor of vascular endothelial cells that has the propensity to arise in various clinical settings. This tumor predominantly occurs in the head and neck region in elderly patients, but it also has been reported to develop postradiotherapy or in the setting of chronic lymphedema in the extremities.1-3 In all settings, the diagnosis carries a very poor prognosis with a high likelihood of local recurrence and rapid dissemination. The mortality rate typically is 80% or higher.2,4-6

Making the correct clinical diagnosis of cutaneous angiosarcoma may be difficult given the variety of patient symptoms and clinical appearances that can be demonstrated on presentation. Lesions can appear as bluish or violaceous plaques, macules, or nodules, and ulceration may be present in some advanced cases.5,7 Clinical misdiagnosis is common, as cutaneous angiosarcomas may be mistaken for infectious processes, benign vascular malformations, and other cutaneous malignancies.1 Biopsy often is delayed given the initial benign appearance of the lesions, and this frequently results in aggressive and extensive disease at the time of diagnosis, which is unfortunate given that small tumor size has been shown to be one of the only favorable prognostic indicators in cutaneous angiosarcoma.1,2,6,8

Microscopically, diagnosis of cutaneous angiosarcoma can present a challenge, as the histology varies between a well-differentiated vascular neoplasm and a considerably anaplastic and poorly differentiated malignancy. On low power, some areas may appear as benign hemangiomas with other areas showing frank sarcomatous features.9 As a result, these tumors can be mistaken for a variety of other diseases including melanomas, carcinomas, or other vascular tumors.6,8,9 Previously, electron microscopy has been utilized on undifferentiated tumors to help distinguish cutaneous angiosarcomas from other potential diagnoses. The atypical tumor cells of cutaneous angiosarcoma display common features of endothelial cells (eg, pinocytotic vesicles, tubulated bodies).7 Historically, it has been noted that the histologic findings and tumor grade provide little evidence regarding the aggressiveness of the tumor, and all cutaneous angiosarcoma diagnoses receive a poor prognosis.6,8

Classically, the histologic findings of cutaneous angiosarcoma include a highly infiltrative neoplasm forming irregular vascular channels that penetrate through the cutaneous soft tissues and frequently extend into the subcutaneous fat. The vascular spaces are lined by hyperchromatic endothelial cells with varying degrees of atypia.1,2,4,6,7,10 Occasionally, prominent endothelial cells lining a papillary structure within the lumen of the neoformed vessel may also be observed. Currently, immunohistochemical staining for MYC, Ki-67, D2-40, and various other markers complement the histologic findings to aid in the diagnosis of cutaneous angiosarcoma.11,12 An additional diagnostic clue that has been described in cases of postirradiation cutaneous angiosarcoma shows free-floating or tufted pleomorphic spindle cells within the vascular lumen (Figure). This finding has been described as “fish in the creek.”11 In this study, we aimed to determine the frequency and subsequent diagnostic utility of the fish-in-the-creek finding in cases of cutaneous angiosarcoma.

Characteristic finding of spindled, atypical endothelial cells projecting into the vascular lumen in a cutaneous angiosarcoma, which has been likened to “fish in the creek” (H&E, original magnification ×100).


A natural language search of our institutional archives over a 20-year period (1997–2017) using the term angiosarcoma was performed. Fifteen cases of cutaneous angiosarcoma were identified. Fifteen additional benign and malignant vascular tumors with cutaneous angiosarcoma in the histologic differential diagnosis were selected from the archives over a similar time frame. The additional lesions included Kaposi sarcoma (n=3), atypical vascular lesion (n=6), atypical hemangioma (n=1), tufted angioma (n=1), epithelioid hemangioma (n=1), epithelioid hemangioendothelioma (n=1), sinusoidal hemangioma (n=1), and angiofibroma (n=1). The pathologists were blinded to the original diagnosis of each case and were instructed to evaluate the histology slides for the sole feature of free-floating intraluminal spindle cells or spindle cells tufting off the endothelium. Epithelial cells lining papillae found within the vessel lumen were not counted as a positive finding, as they do not fit the criteria described for the histologic pattern of fish in the creek. Following microscopic evaluation, the original diagnoses were reassigned to their respective cases to evaluate the diagnostic utility of this feature.

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