feat: cc4k-v0.5.1.1

content/2.cc4k/1.index.md

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 CC4K (Cancer Classifications for Kids) provides a harmonized, computable pediatric cancer classification framework used across [St. Jude Cloud](https://stjude.cloud) and by the [CCDI Federated API](https://github.com/CBIIT/ccdi-federation-api).
 
+## v0.5.1
+
+Submitted: April 14, 2026
+
+Click [here](/files/cc4k/Official_CC4K_v0.5.1.1.xlsx){target="_blank"} to download.
+
+Version 0.5.1 provides a focused incremental update to the CC4K solid tumor hierarchy following the structural revisions introduced in v0.5.
+This release adds four new disease classifications identified through newly curated case studies requiring formal classification within the tree.
+These include the solid tumor entities Dyskeratosis Congenita, Chondromyxoid Fibroma, and Sinonasal Angiofibroma, as well as the hematologic malignancy Primary Mediastinal Large B-cell Lymphoma.
+
+These nodes are introduced to ensure accurate representation of incoming samples and to maintain alignment with the WHO 5th Edition Classification of Tumours: Paediatric Tumours (Pediatric bluebook). No structural reorganization of the tree was performed; rather, this update reflects a measured expansion within the existing Pediatric bluebook, preserving the chapter-based organizational principles established in v0.5.
+
 ## v0.5
 
 Submitted: March 11, 2026