Intra and inter-tumoral heterogeneity in syndromic neuroendocrine tumors

Hereditary endocrine neoplasias, including phaeochromocytoma/paraganglioma (PPGL) and medullary thyroid cancer (MTC), are caused by autosomal dominant mutations in a multitude of familial cancer genes. A common feature of these diseases is the presentation of multiple primary tumours or multifocal disease representing independent tumour clones that have arisen from the same initiating genetic lesion but have undergone independent clonal evolution. Such tumours provide a unique opportunity to discover common co-operative changes required for tumorigenesis while controlling for the genetic background of the individual. We performed an in-depth genomic analysis of synchronous and metachronous tumours from five patients harbouring germline mutations in the genes SDHB, RET and MAX. Using whole exome sequencing and high-density SNP-arrays we analyzed between two and four primary tumours from each patient. Furthermore, we applied multi-regional sampling to assess intra-tumoral heterogeneity and clonal evolution in two cases involving PPGL and MTC, respectively. Heterogeneous patterns of genomic change existed between synchronous or metachronous tumours with evidence of branching evolution. We observed striking examples of evolutionary convergence involving the same rare somatic copy-number events in synchronous primary PPGL. Convergent events also occurred during clonal evolution of metastatic MTC. These observations suggest that genetic or epigenetic changes acquired early within precursor cells, or pre-existing within the genetic background of the individual, create contingencies that determine the evolutionary trajectory of the tumour. The Affymetrix CytoscanHD platform was used to perform copy number profiling on four synchronous paragangliomas from a patient (C1) with a germline SDHB mutation. The Affymetrix CytoscanHD platform was also used to analyse a primary tumour and metastasis from a medullary thyroid carcinoma from a patient (C5) with a germline RET mutation. In addition, the Affymetrix OncoScan platform was used to analyse high interest regions from within the first primary, as well as two additional primary tumours from patient C5.

遗传性内分泌肿瘤（hereditary endocrine neoplasias）涵盖嗜铬细胞瘤/副神经节瘤（phaeochromocytoma/paraganglioma, PPGL）与甲状腺髓样癌（medullary thyroid cancer, MTC），其致病机制为多个家族性癌症基因发生常染色体显性突变。此类疾病的共同特征为患者表现出多原发肿瘤或多灶性病变：这些病变源自同一初始遗传损伤，但各自经历了独立的克隆进化，属于独立的肿瘤克隆。这类肿瘤为探究肿瘤发生所需的协同遗传改变提供了独特的研究模型，同时可控制个体遗传背景这一变量。
本研究对5名携带SDHB、RET及MAX生殖系突变的患者的同步性与异时性肿瘤开展了深度基因组分析。研究采用全外显子组测序与高密度单核苷酸多态性阵列（SNP array）技术，对每位患者的2至4个原发肿瘤进行检测分析。此外，针对分别涉及PPGL与MTC的2个病例，研究应用多区域采样技术评估了肿瘤内异质性与克隆进化情况。
同步性或异时性肿瘤之间存在多样化的基因组改变模式，并伴随分支进化的证据。研究观察到多例显著的进化趋同现象：同步性原发PPGL中出现了相同的罕见体细胞拷贝数事件；转移性MTC的克隆进化过程中也发生了趋同事件。上述结果提示，在前体细胞中早期获得的遗传或表观遗传改变，或是个体遗传背景中预先存在的改变，会构建出决定肿瘤进化轨迹的特定条件。
本研究使用Affymetrix CytoscanHD平台，对1名携带生殖系SDHB突变的患者（C1）的4个同步性副神经节瘤开展拷贝数谱分析。该平台同时被用于分析1名携带生殖系RET突变的甲状腺髓样癌患者（C5）的原发肿瘤与转移灶。此外，研究使用Affymetrix OncoScan平台，对患者C5的首个原发肿瘤以及另外2个原发肿瘤的高关注区域进行了检测分析。