Molecular Calssification of Basal Cell Carcinomas

描述（由申请人提供）：皮肤基底细胞癌是迄今为止美国最常见的癌症类型，占所有新诊断的恶性肿瘤的近一半。虽然这些肿瘤很少导致癌症死亡，但由于局部侵袭和组织破坏，它们与显著的发病率相关。基底细胞癌在肉眼和显微镜下的外观和生物学行为上都是非常多变的，一个常见的组织病理学分类系统将肿瘤分为五大类，它们在侵袭性、预后和对治疗的反应上都不同。我的实验室分离出一个遗传性基底细胞癌的基因（人类补丁；基因符号PTCH），并表明该基因在散发性基底细胞癌中也会发生突变。与视网膜母细胞瘤的双重打击模式完全类似，几乎所有散发性基底细胞瘤都有两个体源性的PTCH失活突变。PTCH是hedgehog信号转导通路的一员。少数缺乏PTCH突变的bcc在smoothened （SMO）中有激活突变，SMO是hedgehog通路的另一个成员，其蛋白通常被补丁蛋白抑制。所有bcc亚型都有PTCH或SMOH突变，这表明这些基因中的一个或另一个突变对bcc的发展至关重要，但并不决定组织学亚型。此外，已知在bcc中发生的其他遗传改变，如p53或RAS基因突变，与生物行为的变化无关。本研究的目的是确定不同组织学亚型基底细胞癌的遗传原因和分子相关性。具体目的是：1)确定PTCH和SMO下游hedgehog通路成员的遗传变异是否导致了这些肿瘤的生物学行为变化；2)作为检测bcc中其他遗传和表观遗传现象的间接方法，使用微阵列分析尝试对这些肿瘤进行分类，并确定一组表达预测其生物学行为的基因。

DESCRIPTION (provided by applicant): Basal cell carcinoma of the skin is by far the most common type of cancer in the United States, representing nearly one half of all newly diagnosed malignancies. Although these tumors infrequently cause cancer mortality, they are associated with significant morbidity due to local invasion and tissue destruction. Basal cell carcinomas are extremely variable in gross and microscopic appearance and biological behavior, and a common histopathologic classification system divides the tumors into five main categories which differ in aggressiveness, prognosis, and response to therapy. My laboratory isolated a gene for hereditary basal cell carcinomas (human patched; gene symbol PTCH) and showed that this gene is mutated in sporadic BCCs as well. Exactly analogous to the two-hit paradigm established for retinoblastoma, almost all sporadic basal cell tumors have two somatically-derived, inactivating PTCH mutations. PTCH is a member of the hedgehog signal transduction pathway. The few BCCs lacking mutations in PTCH have activating mutations in smoothened (SMO), another member of the hedgehog pathway whose protein is normally repressed by the patched protein. All subtypes of BCCs have mutations in PTCH or SMOH, indicating that mutations in one or the other of these genes are essential to the development of BCCs but do not dictate the histologic subtype. Furthermore, other genetic alterations known to occur in BCCs, such as p53 or RAS gene mutations, do not correlate with variation in biologic behavior. The purpose of this study is to identify the genetic causes and molecular correlates of different histologic subtypes of basal cell carcinomas. Specific aims are to 1) determine if genetic variation in members of the hedgehog pathway downstream from PTCH and SMO contribute to variation in biological behavior of these tumors, and 2) as an indirect method of examining other genetic and epigenetic phenomena in BCCs, use microarray analysis to try to classify these tumors and identify a set of genes whose expression predicts their biological behavior.