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Subcutaneous panniculitis-like T-cell lymphoma (SPTCL) is a distinct type of peripheral T-cell lymphoma, which has gained recognition over the past decade. The disease presents complex clinical, pathologic, and immunohistochemical features, which warrant awareness by dermatologists, dermatopathologists, hematopathologists, hematologists, oncologists, and internists. SPTCL was initially included as a provisional entity in the Revised European-American Lymphoma classification, followed by the European Organization for Research and Treatment of Cancer classification as a primary cutaneous lymphoma, and subsequently as a distinct entity by the World Health Organization classification. It is known that patients diagnosed with SPTCL usually respond poorly to therapy, and the tumor progresses aggressively. Data from recent studies in a series of cases of SPTCL by the European Organization for Research and Treatment of Cancer Cutaneous Lymphoma Group have further identified SPTCL as a heterogeneous disease entity, which comprises an alpha/beta subtype (SPTCL-AB) and a gamma/delta subtype (SPTCL-GD). The latter has recently been included in the entity of "cutaneous gamma/delta T-cell lymphoma" by the World Health Organization, Pathology and Genetics of Skin Tumours. The clinical, histologic, and immunophenotypic data, treatment, and prognosis, appear different in the 2 subtypes of SPTCL. We report a case of fatal SPTCL-GD (cutaneous gamma/delta T-cell lymphoma), with detailed clinicopathologic features, immunohistochemical studies, treatment, and clinical course. In view of its aggressive behavior, identification of this disease is critical for proper management and treatment.

Keratoacanthomas are benign skin tumors that grow rapidly but eventually regress. They occur most commonly in sun-exposed skin and are histologically remarkably similar to squamous cancers. Since mutations of the p53 tumor suppressor gene are found frequently in cutaneous squamous cell carcinomas, we hypothesized that p53 mutations might contribute to the development of keratoacanthomas. To address this question, we did p53 immunohistochemistry with a polyclonal rabbit antiserum, CM-1, that binds both mutant and wild-type p53 proteins. Although wild-type p53 protein degrades rapidly and is generally undetected by immunohistochemistry, mutant p53 protein has a longer half-life and accumulates to detectable levels. We tested 26 formalin-fixed keratoacanthomas and 4 normal skin biopsies. Positive nuclear staining was detected in 20 of 26 (77%) of the keratoacanthomas and in none of the normal skin samples. Nuclear staining occurred in the outermost layer of the neoplasms and not in the keratin-filled central cores. Since nuclear p53 protein within a cutaneous squamous cell carcinoma usually correlates with missense mutation, these data suggest that p53 mutations contribute to the development of this benign neoplasm. The histologic similarity to squamous cell carcinoma and the accumulation of p53 protein suggest progression toward malignancy, but the invariable regression of these tumors suggests an arrest at some point in multistage carcinogenesis. If this model is correct, then genetic analysis of keratoacanthomas may provide clues to the later stages of squamous carcinogenesis including local invasion and metastasis.

We present a rare case of metastatic adenocarcinoma of the parotid gland to the skin. Reviewing the histologic features of the primary parotid gland and comparing the microscopic sections and immunohistochemical studies, we concluded the skin tumor to be metastases from the parotid adenocarcinoma. By histologic examination alone, it is difficult to distinguish an eccrine sweat gland carcinoma from a metastatic carcinoma of the salivary gland. Immunohistochemical analysis may not be conclusive. Therefore, clinical history and clinicopathologic correlation are essential in arriving at an accurate diagnosis in these cases.

Subcutaneous panniculitis-like T-cell lymphoma (SPTCL) is a distinct type of peripheral T-cell lymphoma, which has gained recognition over the past decade. The disease presents complex clinical, pathologic, and immunohistochemical features, which warrant awareness by dermatologists, dermatopathologists, hematopathologists, hematologists, oncologists, and internists. SPTCL was initially included as a provisional entity in the Revised European-American Lymphoma classification, followed by the European Organization for Research and Treatment of Cancer classification as a primary cutaneous lymphoma, and subsequently as a distinct entity by the World Health Organization classification. It is known that patients diagnosed with SPTCL usually respond poorly to therapy, and the tumor progresses aggressively. Data from recent studies in a series of cases of SPTCL by the European Organization for Research and Treatment of Cancer Cutaneous Lymphoma Group have further identified SPTCL as a heterogeneous disease entity, which comprises an alpha/beta subtype (SPTCL-AB) and a gamma/delta subtype (SPTCL-GD). The latter has recently been included in the entity of "cutaneous gamma/delta T-cell lymphoma" by the World Health Organization, Pathology and Genetics of Skin Tumours. The clinical, histologic, and immunophenotypic data, treatment, and prognosis, appear different in the 2 subtypes of SPTCL. We report a case of fatal SPTCL-GD (cutaneous gamma/delta T-cell lymphoma), with detailed clinicopathologic features, immunohistochemical studies, treatment, and clinical course. In view of its aggressive behavior, identification of this disease is critical for proper management and treatment.

Ultrastructural studies of Kaposi's sarcoma (KS) from skin biopsies of 24 patients (eight with acquired immunodeficiency syndrome (AIDS) and 16 without) were performed to delineate the nature of hyaline globules and vascular slits. These structures have been regarded as one of the important criteria for the recognition of KS under light microscopy. Histochemical and immunochemical studies were also performed to correlate with the electron microscopic (EM) observations. The most remarkable EM findings of KS were the intracytoplasmic lumen formation and erythrophagocytic activities of the neoplastic cells, particularly in the mature nodular, or neoplastic stage. The spindle-shaped or ovoid neoplastic cells frequently contained one to several intact and fragmented red blood cells. The intracellular and extravasated erythrocytes were often arranged in single files, giving these vascular slits an elongated appearance on longitudinal sections. The phagocytic activities of the neoplastic cells were demonstrated by the presence of membrane-bound lysosomes containing phagocytized erythrocytes and their partially digested forms (erythrophagosomes) adjacent to pinocytotic vesicles, prominent rough endoplasmic reticulum, and Golgi apparatus, as well as scattered, small, membrane-bound lysosomal granules, some of which were attached to the erythrophagosomes. The erythrophagosomes underwent various stages of disintegration. The partially digested red cells varied from 0.4 to 10 microns in diameter. The results of histochemical and immunochemical findings also strongly suggested that erythrophagosomes were most likely the hyaline globules (bodies) seen in light microscopy. The exact mechanism of erythrophagocytosis is uncertain. However, its consequences, erythrophagosomes, and intracytoplasmic lumen formation, particularly in the nodular or neoplastic stage in patients with and without AIDS, are among the important histologic features of KS.

Squamous-cell carcinoma may arise in scars of chronic discoid lupus erythematosus. Although there have been 19 cases reported previously, detailed histopathologic features of this entity have not been recorded. We report a patient with extensive chronic discoid lupus erythematosus involving the scalp with subsequent development of multiple squamous-cell carcinomas. The tumors were locally aggressive with recurrences and invasion into the underlying skull and dura. The patient died of respiratory failure 4 1/2 years after initial surgical treatment. There was no clinical evidence of metastasis. Squamous carcinoma arising in discoid lupus erythematosus can be regarded as a low-grade carcinoma. Although about 20% of patients developed local recurrences and metastasis developed in about 30%, fatality occurred in only two patients (10.5%). Pertinent literature is reviewed, and the histopathologic findings, differential diagnosis, and biologic behavior of this tumor are discussed.

Focal acantholytic dyskeratosis (FAD) is a distinctive histologic pattern characterized by suprabasilar clefts surrounding dermal papillae (villi), acantholytic and dyskeratotic cells at all levels of the epidermis, hyperkeratosis, and parakeratosis. The features of FAD are typically seen in Darier's disease, warty dyskeratoma, and transient acantholytic dermatosis; they are also present in a variety of cutaneous neoplastic and nonneoplastic lesions. FAD, however, has not been previously described in lesions of inflammatory dermatoses. We report a case of FAD occurring in lesions of pityriasis rubra pilaris (PRP). To the best of our knowledge, this is the first reported case of this kind. We also review the pertinent literature.