CHARLESTON, W.Va. (AP) — A panel studying possible links between a chemical used at a DuPont plant in West Virginia and various diseases needs at least three more months to finish its work.

The C8 Science Panel has already concluded there's a probable link to testicular and kidney cancers, and pregnancy-induced hypertension. But in April, it said it had found no link between the chemical, also known as or perfluorooctanoic acid, and 19 other types of cancer.

In a letter sent Monday to Wood County Circuit Court J.D. Beane, the three-member panel said it won't be able to meet a July 31 deadline for assessment reports on 14 other diseases.

While the panel has made substantial progress, it said it underestimated the challenge in resolving borderline cases.

The panel intends to file seven reports with the court July 30 on: asthma; chronic obstructive pulmonary disease; stroke; infectious diseases; thyroid disease; autoimmune disease; and neurologic development in children.

It aims to issue reports on the other seven diseases by the end of October. Those will focus on: liver disease; kidney disease; Parkinson's disease; osteoarthritis; heart disease; hypercholesterolemia; and hypertension.

The letter apologizes for the failure to meet the deadline but notes, "a three-month delay to ensure a more thorough evaluation seems to be in everyone's best interests."

The science panel was formed in 2005 under the settlement of a class-action lawsuit that requires DuPont to spend as much as $235 million on medical monitoring programs to help detect the onset of C8-linked diseases among residents in the settlement.

DuPont, which uses C8 at its Washington Works plant near Parkersburg, W.Va., plans to stop making and using C8 by 2015.