A 2 year old girl who is exposed to the sun has progressive development of dryness of the skin, excessive freckling, and keratoses. Skin fibroblasts cultured from this child are most likely to be defective in which of the following? - Nuclear excision repair of pyrimidine dimers a 65 year old man has a radical prostacetomy and lymph node dissection for adenocarcinoma of the prostate. which of the following features is involved in the grading of this neoplasm - Tumor size A man with a fair complexion develops an ulcerated nodule on his face after prolonged exposure to sunlight. Examination of tissue obtained on excision of the nodule shows invasive squamous cell carcinoma. Which of the following types of DNA damage is most likely responsible for this leason? - Pyrimidine dimers A 45 year old woman with cancer is undergoing an intensive 2 week course of chemotherapy with vinblastine. Which of the following changes is most likely to occur by the end of this treatment? - Decreased number of neutrophils - vinblastin mechanism is to bind microtubular proteins in the mitotic spindle, thereby preventing cell division during metaphase. (anaphase promoting complex inhibitor) An 11 year old boy has had pain in his right mid thigh for 2 weeks. Physical examination shows an area of warmth and tenderness around an ill defined mass. X ray of the femure shows a solitary mid diaphyseal osteolytic lesion with permeative margins. The lesion is surrounded by concentric layers of reactive bone. Tissue obtained on biosy of the mass is composed of poorly differentiated sheets of small, uniform, hyperchromatic cells with a very high nuclear cytoplasmic ratio, scant stroma, and no visible matrix. Which of the following is the most likely diagnosis?