PTEN alteration (sequencing) and PTEN loss (IHC)

aka PTEN loss, PTEN deficiency, PTEN-deficient, PTEN alteration, PTEN deletion, PTEN mutation, PTEN IHC loss, PTEN null

PTEN can be lost by mutation or deletion (read by sequencing) or as absent protein on a stain. Both readouts select capivasertib: alterations in breast cancer, and protein deficiency in metastatic hormone-sensitive prostate cancer.

PTEN loss removes the brake on PI3K signalling. In breast cancer capivasertib with fulvestrant is labelled for tumours with PIK3CA, AKT1 or PTEN alterations by FoundationOne CDx (CAPItello-291); in prostate cancer, following CAPItello-281, the 2026 label adds capivasertib with abiraterone for metastatic androgen pathway modulation-naive or -sensitive prostate cancer selected on PTEN deficiency in tumour tissue by the VENTANA PTEN (SP218) RxDx Assay (P250031, 12 June 2026). The IHC rule is loss of PTEN staining in tumour cells with retained stromal staining; the sequencing rule is a deleterious mutation or homozygous deletion.

Part ofPTEN· PTEN All readouts

PTEN: what it is and how drugs act on it · animated schematic, not to scale

Target · the protein and the cell it sits on
Drug · antibody, small molecule, cell or radioligand
Effect · signal, damage or kill

In plain words · PTEN is the brake on the PI3K growth pathway; when a tumour loses it the pathway runs unchecked, which is why PTEN loss now selects patients for the AKT inhibitor capivasertib.

Sequencing 2 approval thresholds

What it means for a patient

PTEN loss means the PI3K growth pathway is running without its brake. In hormone-receptor-positive breast cancer it qualifies you for capivasertib with fulvestrant after hormone therapy; in newly metastatic hormone-sensitive prostate cancer a PTEN-deficient stain qualifies you for capivasertib added to abiraterone. Ask which test was used, because the breast indication uses sequencing and the prostate one a stain.

Written only from the label or guideline text cited on this page. Not medical advice; your own report and the reading your team gives it come first.

Scoring rule

Sequencing: a deleterious PTEN mutation or deletion in tumour tissue or plasma. Immunohistochemistry: absence of PTEN staining in tumour cells with retained staining in adjacent stroma, on the VENTANA PTEN (SP218) RxDx Assay for prostate cancer.

“PTEN protein Loss/Deficient”
FDA: List of FDA-Authorized Companion Diagnostic Devices

Thresholds used in approvals

Threshold	Drug	Cancer	Regulator	Source
PTEN alteration (with PIK3CA and AKT1 as the qualifying set)	Capivasertib	HR-positive / HER2-negative breast cancer	FDA	label
PTEN deficiency in tumour tissue (IHC)	Capivasertib	Metastatic hormone-sensitive prostate cancer	FDA	label

Drugs whose label names it

Capivasertib

Companion diagnostics (FDA list)

Device	Maker	Indication and sample	Drug	PMA / 510(k)
FoundationOne CDx	Foundation Medicine	Breast Cancer - Tissue	Capivasertib Fulvestrant	P170019/S048 (11/16/2023)
VENTANA PTEN (SP218) RxDx Assay	Ventana Medical Systems (Roche Tissue Diagnostics)	Metastatic hormone-sensitive prostate cancer (mHSPC) - Tissue	Capivasertib	P250031 (06/12/2026)

Tests that measure it

FoundationOne CDx Tempus xT and xT CDx FoundationOne CDx FoundationOne Liquid CDx Caris MI Profile

Trials that name this readout

Matched on the name and aliases of the readout in the title, setting and summary of each trial; a match is a mention, not proof the readout was an entry criterion.