---
schema_version: "secwatch.filing_event.v1"
accession: "0001447362-21-000239"
form_type: "8-K"
ticker: "CSTL"
cik: "0001447362"
company_name: "CASTLE BIOSCIENCES INC"
filed_at: "2021-10-19T23:59:59+00:00"
generated_at: "2026-06-28T19:56:55.923681+00:00"
event_type: "m_and_a"
sentiment: "positive"
materiality_score: 0.75
calibrated_materiality_score: 0.75
confidence: "high"
source: SEC EDGAR
---

# Castle Biosciences to acquire Cernostics for up to $80M; expands into GI diagnostics with TissueCypher

## Summary
- Upfront consideration of $30M (cash or $20M cash + $10M stock at Castle's discretion); up to $50M in milestones based on 2022 performance.
- Cernostics' TissueCypher Barrett's Esophagus Assay is first precision medicine test to predict progression to esophageal cancer in BE patients.
- Deal expands Castle's estimated U.S. TAM by approximately $1B, complementing its dermatologic franchise.
- Transaction expected to close prior to year-end 2021; Cernostics management to remain; operations stay in Pittsburgh.

## SEC filing metadata
- accession: 0001447362-21-000239
- form_type: 8-K
- ticker: CSTL
- cik: 0001447362
- company_name: CASTLE BIOSCIENCES INC
- filed_at: 2021-10-19T23:59:59+00:00
- event_type: m_and_a
- sentiment: positive
- materiality_score: 0.75
- calibrated_materiality_score: 0.75
- confidence: high
- sec_items: 1.01, 7.01, 8.01, 9.01
- EDGAR index: https://www.sec.gov/Archives/edgar/data/1447362/000144736221000239/0001447362-21-000239-index.htm
- EDGAR primary document: https://www.sec.gov/Archives/edgar/data/1447362/000144736221000239/cstl-20211018.htm

## Machine-readable alternates
- HTML: https://secwatch.observer/filing/0001447362-21-000239
- JSON: https://secwatch.observer/filing/0001447362-21-000239.json
- Plain text: https://secwatch.observer/filing/0001447362-21-000239.txt

This AI-assisted summary is a reading aid. Review the linked SEC EDGAR filing before relying on any specific claim.