Sarcomas

Primary sarcomas of the penis are rare, representing less than 5% of all penile cancers and about 2% of all genitourinary sarcomas.27 101-104 They can be classified into superficial and deep-seated tumors depending on whether they are located above or below the tunica albuginea (in the penile shaft) or invade the corpus spongiosum of the glans.105 The superficial tumors are usually of low grade with a small tendency for nodal metastasis and systemic dissemination while deep-seated sarcomas are biologically more aggressive and associated with a dismal prognosis.27 Ominous prognostic factors include larger size (>5 cm), deep location (corpus cavernosum and spongiosum), high-grade histology, incomplete surgical resection, positive surgical margins, presence of metastatic disease, and pRB expression^7-101-106-107 The most common penile sarcoma is Kaposi's sarcoma, followed by leiomyosarcomas.27108

Other malignant soft-tissue tumors of the penis have been reported and their morphological and immunohistochemical features are similar to those found elsewhere in the body.27-108-109

Kaposi's sarcoma preferentially affects patients with human immunodeficiency virus (HIV) infection although it has been reported in HIV-negative individuals.105 108 110-115 In patients with acquired immunodeficiency syndrome (AIDS), a population commonly associated with this malignancy, up to 20% of all Kaposi's sarcomas affect the genital area.28116 The glans penis is the most common location but it may also affect the coronal sulcus, foreskin, or skin of the shaft.115 Clinically, it presents as erythematous maculae to lilaceous plaques and nodules. Histological features are similar to those described elsewhere and include a patch, plaque, and nodular stage (Fig. 3.19b). In the patch stage a subtle proliferation of slit-like and/or angulated jagged vessels is seen between collagen bundles. Extravasated erythrocytes, hemosiderin-laden macrophages and an inflammatory infiltrate of lymphocytes and plasma cells are also observed. An important morphological clue of Kaposi's sarcoma is the "promontory sign" in which newly formed vessels protrude into the lumen of pre-existing ones. In the plaque stage the vascular proliferation is more diffuse and prominent spindle cells begin to appear between the vessels. Intracytoplasmic and extracellular PAS-positive hyaline globules may also be seen. The nodular stage is characterized by confluence of neoplastic spindle cells to form well-defined nodules with a storiform pattern of growth. Slit-like spaces containing erythrocytes are readily found. Dilated blood vessels, hemosiderin-laden macrophages, and an evident inflammatory infiltrate are commonly observed at the periphery. The main differential diagnoses include benign and malignant vascular tumors and tumors with a fusiform pattern of growth.27 Neoplastic cells in Kaposi's sarcoma are positive for CD31 and CD34 and negative for desmin, allowing its distinction from other nonvascular fusiform tumors. In problematic cases, identification of human herpes virus 8 (HHV-8) is helpful for confirming the diagnosis.

Leiomyosarcomas preferentially involve the shaft or penile base and are more likely to be superficial than deep-seated.102 105 108 117 The typical gross aspect is of a white-to-tan firm tumor with irregular borders. Microscopically, tumors are composed of spindle cells with abundant eosinophilic cytoplasm, focal juxtanuclear vacuoles, and blunt-ended nuclei with evident atypias (Fig. 3.19c). Atypical changes range from moderate to severe and anaplastic giant cells are not unusual. Mitoses are easily found and can be numerous. Myxoid changes can also be noted in some cases. Neoplastic cells are positive for muscle-specific actin, a-smooth muscle actin, and desmin. Differential diagnosis of penile leiomyosarcoma includes leio-myoma, myointimoma, nodular Kaposi's sarcoma, malignant fibrous histiocytoma, and sarcomatoid carcinoma. Penile leiomyoma is an exceedingly rare tumor which is histologically similar to other leiomyomas in other anatomical locations.104 108 118 Myointimoma can simulate a leiomyosarcoma for its fusiform/plexiform pattern of growth but neoplastic cells are devoid of significant cytological atypias and exhibit positivity for muscle-specific actin (HHF-35), a-smooth muscle actin, and calponin but minimal reactivity for desmin.119-121 Nodular Kaposi's sarcoma can be confused with superficial leiomyosarcoma, especially by its atypical spindle cell pattern of growth, but the H&E morphology and immunophenotype of neoplastic cells allow a proper diagnosis. Sometimes a malignant melanoma can exhibit a predominant storiform pattern of growth and be similar to a leiomyosarcoma. The presence of more typical melanoma areas elsewhere and positivity for melanocytic markers helps in the distinction. Malignant fibrous histiocytoma is an exclusion diagnosis and should be established only when other tumors have been ruled out.109 Finally, considering that sarcomatoid carcinoma is a far more prevalent tumor than true penile leiomyosarcoma differential diagnosis should include this SCC variant as well. The presence of epithelial nests within the tumor mass, associated areas of PeIN, and pattern of immunoexpression are helpful clues for distinguishing these two tumors.14,15

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