Molecular Calssification of Basal Cell Carcinomas

描述(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有关。基底细胞癌在大体和显微镜下的形态和生物学行为差异很大，常见的组织病理学分类系统将肿瘤分为五个主要类型，这些类型在侵袭性、预后和治疗反应方面存在差异。我的实验室分离了一个遗传性基底细胞癌的基因(人补丁；基因符号PTCH)，并表明该基因在散发性基底细胞癌中也发生了突变。与为视网膜母细胞瘤建立的两次打击范例完全相似，几乎所有散发性基底细胞肿瘤都有两个躯体来源的、失活的PTCH突变。PTCH是Hedgehog信号转导通路的成员。少数在PTCH中缺乏突变的BCC在平滑(SMO)中有激活突变，SMO是刺猬途径的另一个成员，其蛋白通常被补丁蛋白抑制。所有BCC亚型都有PTCH或SMOH突变，这表明其中一个基因的突变对BCC的发展是必不可少的，但并不决定组织学亚型。此外，已知发生在基底细胞癌中的其他基因改变，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的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下游刺猬通路成员的遗传变异是否导致这些肿瘤的生物学行为的差异；2)作为检查BCC中其他遗传和表观遗传现象的间接方法，使用微阵列分析试图对这些肿瘤进行分类，并识别一组其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.