Diagnostic Assays to Plan Specific Drug Treatment

Elizabeth Hammond MD

Criteria for Development of Diagnostic assays

• Defined assay characteristics for total test• Standardized procedures for assay, reference

materials and training plan to assure initial and ongoing competence

• Acceptable interlaboratory variability evaluated in standard manner, possibly using TMA’s

• Plan for new laboratory validation• Plan for ongoing laboratory competence

assessment

Assay Characteristics

• Specimen adequacy: definition of unacceptable samples

• Specimen handling: time from surgery to processing, time in fixative, temperature

• Standardized Reference Materials• Assay conditions: precise, clearly reported • Interpretation and reporting criteria: precise,

including how reference material is used in the evaluation and acceptable limits of interobserver variation

CAP FISH Survey Results

FISH amplified

2000: 35 participants

35/35 = amplified

2001: 63 participants

58/63= amplified

(others= no response)

FISH non amplified

2000: 35 participants

35/35= non amplified

2001: 63 participants

49/63= non amplified

(others= no response)

CAP CYH survey results, 2000-2001

CAP IHC (MK) Survey

FISH amplified case

357 participants

IHC scores:

0 19 (3.7%)

1+ 4

2 + 52

3 + 296

FISH unamplified case

380 participants

IHC scores:

0 275

1+ 69

2+ 27 (7%)

3+ 10 (3%)

Source: 2000 CYH 01, 02 and MK Surveys, CAP

CAP MK B Survey Image Scoring

Photo Score 0 1+ 2+ 3+ Total

01 1+ 25 352 80 0 457

02 2+ 0 60 376 20 436

03 3+ 8 0 3 445 456

04 1+ 92 350 13 0 455

06 2+ 7 133 282 33 455

Score not provided for all images by all participants

FISH vs IHC

• Specimen handling, adequacy not specified for either assay type; DNA less affected than protein

• FISH for Her2 has internal standard (Chr 17) • Standard procedures and training are mandatory

for laboratories performing FISH, but not required for all IHC assays

• Interpretation criteria are quantitative and clearly specified for FISH, ambiguous for IHC

Conclusions

Use of central laboratory during pivotal trial is necessary if there is not assay method standardization, standardized reference materials and training plans for assay and interpretation

Interlaboratory comparison of assay and interpretation criteria should be conducted concurrently with pivotal trial

Validated assay with standardized reference materials, training plan, and interpretation criteria is required prior to Phase III trial

Treatment Guidelines for Patients with Negative Assay Results

• Assay should not be used to assign treatment if:– Relationship between analyte and drug efficacy

is unclear– Interpretation guidelines of assay do not clearly

specify cut point of positive and negative – Assay method is non validated – Standardized reference materials are not

available

Package Insert Information

• Specific information about specimen adequacy and handling parameters

• Assay performance characteristics with assay comparisons, where appropriate

• Assay interpretation guidelines• Acceptable methods of assay validation in a lab• Acceptable levels of interlaboratory variability• Requirement of laboratory participation in

ongoing competency assessment

Assay Utility Assessment

• Phase III clinical trials should be used to assess assay utility

• Tissue banking on such trials should be mandatory so that new assays can be validated on the same specimens

• TMAs can be created to promote new assay utility assessment while optimizing tissue bank specimen use.

TMA Concordance with Slides Arrays Head/Neck Glioma Prostate

One array 90% 86% 86%

Two arrays 95% 93% 93%

Three arrays 99% 95% 93%

Four arrays 100% 97% 97%

RTOG Study, presented USCAP, 2001; N= 150 tumors