Almost a quarter of a century has passed since mesenchymal chondrosarcoma, a rare, insufficiently studied and still poorly understood cartilage neoplasm has been described. Based on 35 cases diagnosed and treated at this Cancer Center, this study found 20 males and 15 females with an average age of 26 years (range, 6–70 years). All but five of the tumors arose in the skeleton in the femur, humerus, and ilium in five cases each, while the os calcis (a rare site for any other osseous tumor) gave rise to this tumor in four instances. Pain was the cardinal symptom in 27 patients. The lesional size varied from 4 to 18 cm (average, 9.5 cm). Histologic examination revealed nine of the tumors to be of the small cell undifferentiated types while the others were of the “hemangiopericytomatoid” variant. According to this subclassification, patients with the small cell type of lesions responded to combination chemotherapy and irradiation, as usually do other small cell sarcomas. The addition of surgical resection may be of value especially in the patients with the hemangiopericytomatoid variant. Preliminary results in the treatment of five such patients with evaluable disease suggest that this combined treatment approach is encouraging. Follow‐up analysis of all patients revealed a 37.9 months median survival, and 28% to be alive at ten years.

This paper describes 6 instances of a peculiar malignant angioendothelioma of the skin in children. Microscopically, the neoplasm is characterized by remarkable, bizarre, intravascular papillary proliferations of atypical endothelium. The tumor is locally invasive and has a potential to metastasize. In spite of this, as far as we know, none of the children have died. All our patients are living and well, free from recurrence and metastases 4 to 16 years after last surgical treatment. The present study was undertaken to demonstrate this curious variant of malignant angioendothelioma in childhood, which has a limited degree of malignancy.

The Dąbska tumor is a rare low-grade angiosarcoma also known as malignant endovascular papillary angioendothelioma of childhood. It primarily affects the skin of children and has a distinctive histologic pattern of anastomosing vascular channels with intravascular papillary outpouchings projecting, sometimes, in a glomerulus-like pattern, into a lumen lined by atypical columnar endothelial cells. Since its original description 30 years ago by one of us, knowledge in this area has expanded.

Parachordoma is a tumor that was established and described by Laskowski in 1951. It is a rare tumor, which appears adjacent to tendons, synovium, and even osseous structures. It is lobular and pseudoencapsulated. Histologically, in some ways, it is compatible with the chordomas of bone with a constant fibrous tissue component. It grows slowly and is only locally invasive. If not adequately excised, it is prone to recur, but complete surgical removal is usually possible. Its exact histogenesis remains obscure. This tumor may have some relationship to the great vesicular cells of chordoid tissue described by Schaffer as "blasige Zellen von chordoiden Gewebe" developing from special synovial cells. Ten cases collected over a period of 26 years at the Institute of Oncology in Warsaw are presented.

The pathology, clinical course, and microscopic appearance of aneurysmal bone cyst are discussed with emphasis on details which distinguish this entity from similar tumors. The radiologic appearance is briefly described and roentgenograms of 13 tumors at different stages of development are presented. The problem of pathogenesis is discussed.

It has been almost a quarter of a century that this rare, still poorly understood and to date insufficiently studied, cartilage neoplasm was described. Based on 19 cases in the young representing 26 percent of chondrosarcoma patients under the age of 21 years, this study found equal sex distribution with the youngest patient being a 6-year old boy. Twelve lesions occurred between the ages of 16 and 21 years. All but one of the tumors arose in the skeleton with nearly half of them involving the lower extremity. Pain was inconsistent and rare at presentation in contrast to the regularity of swelling or a painless mass. Survival analysis revealed a 46 percent 2-year and a 35 percent 5-year survival rate, whereas at 10 years only 20 percent of the patients were still alive. This study attempts to establish the likeliest evolutionary pathway of neoplastic cell differentiation and traces the origin of this tumor to a neoplastic caricature of embryonal endochondral osteogenesis.

Twelve cases of a peculiar, relatively uncommon, benign but locally invasive tumor occurring in the skin of the scalp and mocha are reported. The neoplasm occurs primarily in elderly women and only exceptionally in men. Its growth is very slow and usually many years elapse before the patient comes under treatment; thus, the tumor may attain a huge size. These deeply invasive neoplasms do not metastasize but may recur if not completely excised. Morphologically, it is an epithelial keratinizing growth clearly showing differentiation into the pilosebaceous structures, especially into the outer sheath of the hair follicle. It does not correspond to the “pilomatrixoma” of Forbes and Helwig (calcifying epithelioma of Malherbe) and constitutes a distinct clinicopathologic entity.

Aneurysmal bone cyst may arise in some patients with fibrous dysplasia of bone. The available material of aneurysmal bone cysts has been reviewed. In two cases, the coexistence of fibrous dysplasia and aneurysmal bone cyst was histologically confirmed. The secondary character of the aneurysmal bone cyst in relation to the fibrous dysplasia has been traced. We regard the aneurysmal bone cyst as a peculiar, non‐neoplastic tumor secondary to a preexisting bone lesion. Among the superimposed pathologic conditions on which the aneurysmal bone cyst may take place is fibrous dysplasia of bone.