---
schema_version: "secwatch.filing_event.v1"
accession: "0001447362-21-000262"
form_type: "8-K"
ticker: "CSTL"
cik: "0001447362"
company_name: "CASTLE BIOSCIENCES INC"
filed_at: "2021-12-03T23:59:59+00:00"
generated_at: "2026-06-28T03:48:14.558965+00:00"
event_type: "other_material"
sentiment: "neutral"
materiality_score: 0.35
calibrated_materiality_score: 0.35
confidence: "high"
source: SEC EDGAR
---

# Castle Biosciences extends Phoenix office leases through April 2033, adds 2,564 sq ft

## Summary
- 3707 Lease amended: term extended 61 months to April 2033; premises expanded by 2,564 sq ft to 17,752 total.
- Base rent at 3707 starts at $20.50/sq ft/year ($30,326.33/mo) with annual $0.50/sq ft increases.
- 3737 Lease amended: term extended 69 months to April 2033; base rent unchanged until Aug 2027 then $23.50/sq ft/year.
- Rent abatement for first full calendar month after 3707 expansion commencement.
- Lease amendments involve two properties with Landlord Alturas Siete I and II, LLC.

## SEC filing metadata
- accession: 0001447362-21-000262
- form_type: 8-K
- ticker: CSTL
- cik: 0001447362
- company_name: CASTLE BIOSCIENCES INC
- filed_at: 2021-12-03T23:59:59+00:00
- event_type: other_material
- sentiment: neutral
- materiality_score: 0.35
- calibrated_materiality_score: 0.35
- confidence: high
- sec_items: 1.01, 9.01
- EDGAR index: https://www.sec.gov/Archives/edgar/data/1447362/000144736221000262/0001447362-21-000262-index.htm
- EDGAR primary document: https://www.sec.gov/Archives/edgar/data/1447362/000144736221000262/cstl-20211129.htm

## Machine-readable alternates
- HTML: https://secwatch.observer/filing/0001447362-21-000262
- JSON: https://secwatch.observer/filing/0001447362-21-000262.json
- Plain text: https://secwatch.observer/filing/0001447362-21-000262.txt

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