UNPUBLISHED

UNITED STATES COURT OF APPEALS
                 FOR THE FOURTH CIRCUIT


HALIA S. MARSH, Executrix of the          
estate of Robert Sidney Marsh,
                  Plaintiff-Appellant,
                  v.
                                             No. 98-1943
W. R. GRACE & COMPANY; FRIT
INDUSTRIES, INCORPORATED;
CONTINENTAL CASUALTY COMPANY,
               Defendants-Appellees.
                                          
THEODORE C. MCLEOD,                       
               Plaintiff-Appellant,
                  v.
W. R. GRACE & COMPANY; FRIT                  No. 98-1944
INDUSTRIES, INCORPORATED;
CONTINENTAL CASUALTY COMPANY,
               Defendants-Appellees.
                                          
THOMAS R. SPEER,                          
                   Plaintiff-Appellant,
                  v.
W. R. GRACE & COMPANY; FRIT                  No. 98-1945
INDUSTRIES, INCORPORATED;
CONTINENTAL CASUALTY COMPANY,
               Defendants-Appellees.
                                          
2               MARSH v. W. R. GRACE & COMPANY
            Appeals from the United States District Court
     for the Middle District of North Carolina, at Rockingham.
             N. Carlton Tilley, Jr., Chief District Judge.
              (CA-90-613-3, CA-91-47-3, CA-91-48-3)

                    Argued: January 25, 2000

                   Decided: November 19, 2003

    Before WIDENER, LUTTIG, and MICHAEL, Circuit Judges.



Affirmed by unpublished opinion. Judge Widener wrote the opinion,
in which Judge Luttig and Judge Michael concurred.



                           COUNSEL

ARGUED: John Randolph Ingram, Asheboro, North Carolina, for
Appellants. Jonathan A. Berkelhammer, SMITH, HELMS, MULLISS
& MOORE, L.L.P., Greensboro, North Carolina, for Appellee Frit
Industries; B. Gordon Watkins, III, KILPATRICK STOCKTON,
L.L.P., Winston-Salem, North Carolina, for Appellees W.R. Grace
and Continental Casualty. ON BRIEF: James D. Cowan, Jr., SMITH,
HELMS, MULLISS & MOORE, L.L.P., Greensboro, North Carolina,
for Appellee Frit Industries; Steve M. Pharr, KILPATRICK STOCK-
TON, L.L.P., Winston-Salem, North Carolina, for Appellees W.R.
Grace and Continental Casualty.



Unpublished opinions are not binding precedent in this circuit. See
Local Rule 36(c).
                 MARSH v. W. R. GRACE & COMPANY                       3
                              OPINION

WIDENER, Circuit Judge:

   Plaintiffs Halia S. Marsh, executrix of the estate of Robert Sidney
Marsh, Thomas R. Speer, and Theodore McLeod, executor of the
estate of Beulah M. McLeod, appeal from the district court’s decision
granting summary judgment to defendants W.R. Grace & Co.
(Grace), Frit Industries, Inc. (Frit), and Continental Casualty Com-
pany. Marsh v. W.R. Grace & Co., No. 3:90CV00613 (M.D.N.C.
May 26, 1998). Plaintiffs brought a product liability action against the
defendants stemming from their use of fertilizer contaminated with
the chemical picloram. They alleged that the picloram caused Marsh,
Speer, and Mrs. McLeod to develop cancer. The plaintiffs had one
expert, Dr. Scott Levin, who testified that the contaminated fertilizer
caused the plaintiffs’ cancers. The district court found that Dr.
Levin’s testimony did not satisfy the admissibility requirements for
expert testimony required by the Supreme Court in Daubert v. Mer-
rell Dow Pharmaceuticals, Inc., 

 (1993), and conse-
quently, granted the defendants’ motions for summary judgment
because the plaintiffs provided no additional evidence that the
picloram caused their injuries. Plaintiffs appeal from that decision and
from the district court’s denial of the motions of Mrs. Moore and
Speer to amend their complaints to include chemicals other than
picloram as the cause of their injuries. Marsh v. W.R. Grace & Co.,
No. 3:90CV00613 (M.D.N.C. Oct. 13, 1992); Speer v. W.R. Grace &
Co., No. 3:91CV00048 (M.D.N.C. Dec. 9, 1994). For the reasons set
forth below, we affirm the decisions of the district court.

                                   I.

   The underlying facts of this case are not complicated and largely
not in dispute. Because we are reviewing disposition of this case on
summary judgment, we examine the facts as found by the district
court after it construed the case in the light most favorable to the
plaintiffs. Beall v. Abbott Lab., 

, 618-19 (4th Cir. 1997).
In 1984, Grace manufactured and sold Gold Dollar tobacco fertilizer
using a micronutrient mix provided by Frit which included picloram.
All of the plaintiffs are North Carolina farmers — Marsh and Speer
worked on Marsh’s son’s, Waymon Marsh’s, farm, and the McLeods
4                 MARSH v. W. R. GRACE & COMPANY
worked on their own farm. The plaintiffs purchased and used, either
or both, Grace’s Gold Dollar fertilizer on tobacco crops and on vege-
table gardens. Each of the plaintiffs subsequently discovered that the
Gold Dollar fertilizer contained several ingredients it should not have,
including picloram, a broadleaf herbicide. For several years, the plain-
tiffs were exposed to the picloram while handling the fertilizer itself,
from contact with soil and water contaminated by picloram from the
fertilizer, by eating vegetables from gardens contaminated by the fer-
tilizer, and from eating fish from a pond contaminated by fertilizer
run-off.

   Between 1984 and 1988, all of the plaintiffs suffered from some
type of cancer. Marsh was diagnosed with lung cancer in October
1988, and he died two weeks later at the age of 78. Speer discovered
he had colorectal cancer in March 1988 at the age of 65, but he
received successful treatments for the disease. Mrs. McLeod was
diagnosed with cervical cancer in August 1986. She died from the dis-
ease two years later at the age of 74.

   In 1990, each of the plaintiffs filed their suits against Frit, Grace,
and Continental Casualty Company in North Carolina state court. All
three complaints alleged that the defendants failed to warn the plain-
tiffs of the contaminated fertilizer, made false representations con-
cerning the contaminants in the fertilizer, negligently manufactured
the fertilizer, breached their express and implied warranties, and par-
ticipated in unfair settlement practices. The plaintiffs all claimed dam-
ages incurred as a result of their respective cancers, which they
alleged were proximately caused by the picloram in the fertilizer.

   The defendants removed all three cases to federal court in Decem-
ber 1990. The parties then engaged in extensive discovery, including
an exhaustive deposition of the plaintiffs’ expert witness, Dr. Levin.
On October 28, 1991, the defendants moved for summary judgment
in the Marsh case. In March 1992, Mrs. Marsh made a motion pursu-
ant to Federal Rule of Civil Procedure 15(a) to amend her complaint
to include chemicals other than picloram, specifically 2,4-D. The
court declined her motion on the basis that she had unduly delayed
making the motion and that the defendants would be unfairly preju-
diced if it was granted. In October 1994, soon after the close of dis-
covery, Speer made a motion to amend his complaint under Rule
                  MARSH v. W. R. GRACE & COMPANY                       5
15(a) that was essentially identical to the one Mrs. Marsh had previ-
ously made. In November 1994, the defendants filed motions for sum-
mary judgment in the Speer and McLeod cases. The court denied
Speer’s motion to amend his complaint citing the same reasons it
denied Mrs. Marsh’s motion in addition to the fact that the parties had
again reached summary judgment stage in the proceedings. On May
26, 1998, after reviewing the defendants’ motions for summary judg-
ment in all three cases, the district court found that Dr. Levin’s testi-
mony that picloram caused the plaintiffs’ cancers did not meet the
requirements for admissibility of expert testimony set forth in Dau-
bert. Marsh v. W.R. Grace & Co., No. 3:90CV00613, slip op. at 12
(M.D.N.C. May 26, 1998). Without Dr. Levin’s testimony, the district
court found that there was no genuine issue of material fact with
respect to proximate causation and granted the defendants’ motions
for summary judgment. Marsh, No. 3:90CV00613, slip op. at 3-5.
The plaintiffs now appeal the district court’s exclusion of Dr. Levin’s
testimony and denial of their requests to amend their complaints.

                                   II.

                                   A.

   We review a district court’s decision granting a motion for sum-
mary judgment de novo. Metropolitan Life v. Pettit, 

,
860 (4th Cir. 1998). The district court’s decision on the motion for
summary judgment in this case turned on the exclusion of expert testi-
mony under Daubert. We review a district court’s decision to exclude
expert testimony for abuse of discretion. General Elec. Co. v. Joiner,

, 139 (1997). We first address the plaintiff’s contention
that the district court erroneously excluded Dr. Levin’s testimony and,
second, the court’s subsequent decision to grant summary judgment
for the defendants.

   In Daubert, the Supreme Court set forth the two-part inquiry a dis-
trict court must engage in when determining whether to admit expert
testimony. The district court must exercise a gatekeeping function in
which it only admits expert testimony that is both reliable and rele-
vant. Daubert, 509 U.S. at 589. We are only concerned with the reli-
ability prong of the test in this case because the evidence was relevant
to the causation element of the plaintiffs’ case.
6                 MARSH v. W. R. GRACE & COMPANY
   The Daubert analysis is a flexible one, Daubert, 509 U.S. at 592-
93, 594-95, and, to aid courts engaging in the reliability analysis, the
Court provided four non-exclusive factors that the district court could
consider when evaluating proposed expert testimony: (1) whether the
evidence can be tested, (2) whether the theory has been subjected to
peer review or publication, (3) the known or potential rate of error of
the technique, and (4) whether the relevant scientific community has
generally accepted the theory. Daubert, 509 U.S. at 593-94. The focus
of the district court’s inquiry should be the principles and methodol-
ogy of the expert, not the conclusions reached. Daubert, 509 U.S. at
595. The overall goal of the Daubert analysis is to ensure that "an
expert, whether basing his testimony upon professional studies or per-
sonal experience, employs in the courtroom the same level of intellec-
tual rigor that characterizes the practice of an expert in the relevant
field." Kuhmo Tire Co. v. Carmichael, 

, 152 (1999).

   The Court instructs us to provide district courts with "broad lati-
tude," p.142, or "considerable leeway," p.156, both as to the method
used to decide whether to admit expert testimony and to the decision
whether to admit or exclude the testimony. Kuhmo Tire, 526 U.S.
pp.142, 156. Under the abuse of discretion standard, we examine the
record and the rationale of the district court and reverse its decision
only if it made a clear error in judgment. Westberry v. Gislaved
Gummi AB, 

, 261 (4th Cir. 1999). We are of opinion that
the record supports the district court’s analysis and decision to
exclude Dr. Levin’s testimony.

   Our review of the district court’s opinion discloses that the court
found Dr. Levin’s methods and logical processes used to reach his
opinion on causation were unreliable. Dr. Levin is a medical doctor
specializing in pathology, immunology, and cancer who has
researched and written about cancer. In determining the cause of his
patients’ cancers, Dr. Levin relies on his evaluation of individual
responses to a given intrusive agent. His theory is that all disease is
a function of the host, not of the etiologic agent. So, if the body is set
up for cancer, then the etiologic agent can cause cancer. Dr. Levin
does not focus on epidemiological studies, which indicate percentages
of cancer occurrences from particular causes in designated popula-
tions to aid scientists in determining whether a specific agent can
cause cancer. We have held that that epidemiological evidence is not
                  MARSH v. W. R. GRACE & COMPANY                       7
necessarily required for a valid expert opinion on causation so long
as the expert’s methods are otherwise sound. Benedi v. McNeil-
P.P.C., Inc., 

, 1384 (4th Cir. 1995). However, the district
court, in the case at hand, engaged in a lengthy analysis of Dr. Levin’s
methods using each of Daubert’s four suggested factors and found
that Dr. Levin’s methods were not reliable.

   Daubert first suggests that we should evaluate whether an expert’s
opinion is subject to testing. Daubert, 509 U.S. at 593. The district
court found that Dr. Levin’s testimony was not subject to testing
because he started from the conclusion that picloram caused the plain-
tiffs’ cancers and then generated, without testing, the hypotheses to
support that conclusion. Marsh v. W.R. Grace & Co., No.
3:90V00613, slip op. at 7 (M.D.N.C. May 26, 1998). The record sup-
ports the district court’s decision that Dr. Levin’s opinion is unreli-
able because it cannot be tested or verified consistently, and therefore,
the court did not abuse its discretion.

   Dr. Levin used the results of only one laboratory test performed on
two of the plaintiffs to reach his opinion on causation. This test, how-
ever, did not identify the agent that caused the plaintiffs’ cancers. Dr.
Levin provided no other medical tests to verify his hypothesis that
picloram caused the plaintiffs’ cancers. We conclude that the district
court did not abuse its discretion when it found that Dr. Levin needed
more verification for his opinion because the defendants proposed
several alternative causes for the plaintiff’s cancers. The defendants
presented evidence that showed the plaintiffs had been exposed to a
multitude of chemicals that could cause cancer during their lifetimes,
that one plaintiff had a family history of the type of cancer he con-
tracted, and that another contracted lung cancer after a 50-year history
of smoking. Dr. Levin, however, failed to verify or provide a means
to verify his conclusion by ruling out any alternative causes for the
plaintiffs’ cancers. While an expert need not rule out all alternative
causes to provide a valid opinion, he must at least explain why his
opinion remains sound in light of alternative causes proposed by the
other parties. Westberry v. Gislaved Gummi AB, 

, 265-
66 (4th Cir. 1999). This record supports the district court’s finding
that he did not do so adequately.

  The district court also found that Dr. Levin’s testimony failed the
second Daubert factor because his theories underlying his conclusion
8                 MARSH v. W. R. GRACE & COMPANY
had not been subject to peer review or publication. Marsh, No.
3:90V00613, slip op. at 10. While we acknowledge that the Daubert
analysis must be flexible and that not all medical experts’ theories and
methods will need to be published or peer reviewed, this is a valid
consideration in considering the facts of a particular case. Dr. Levin’s
determination that picloram is a carcinogen is inapposite to much of
the scientific literature on the subject. Neither the National Toxicol-
ogy Program nor the Environmental Protection Agency have listed
picloram as a carcinogen. To support his conclusion that picloram is
a carcinogen, Dr. Levin stated that he read abstracts of several articles
and looked at other studies. But in the face of literature and findings
contradictory to Dr. Levin’s determination, the district court did not
abuse its discretion in finding that Dr. Levin needed further support
for his independent conclusion that picloram causes cancer.

   The district court noted that Daubert’s third factor, the potential
rate of error of a technique, is not directly applicable to Dr. Levin’s
testimony because his technique is not susceptible to a measurable
rate of error. However, we find that the district court did not abuse
its discretion in deciding that Dr. Levin’s failure to identify a no-
effect level for picloram, and his untested assumptions with respect
to the amounts of pecloram to which plaintiffs were exposed, intro-
duce an unacceptable potential for error into his opinion that the
amount of picloram to which plaintiffs were exposed caused their
cancers. While Dr. Levin agreed that picloram had a no-effect level,
he did not state what it was or whether the amounts plaintiffs were
exposed to exceeded that level. Apparently he assumed that the plain-
tiffs’ exposure to the chemical was about three years, and he assumed
the plaintiffs had received adequate exposure to picloram to cause
cancer. We find that the record supports the district court’s decision
that this means of analysis by assumption could lead to an unaccept-
able potential for error.

   After reviewing Dr. Levin’s affidavits and deposition testimony,
we find sufficient support for the district court’s determination that
Dr. Levin’s methods are not generally accepted by the medical com-
munity, the final Daubert factor. While plaintiffs argue that Dr. Levin
relies on a methodology used by other immunologists and cite a por-
tion of an article in the Journal of the American Medical Association
in support of that contention, the article only supports Dr. Levin’s
                  MARSH v. W. R. GRACE & COMPANY                       9
proposition that population studies are not determinative. While
potentially true, the district court, supported by the record, found that
Dr. Levin did not demonstrate that his methods used in this case are
also used by experts in his field. Additionally, the record supports the
district court’s conclusion that Dr. Levin’s opinion that picloram is a
carcinogen is not generally accepted in the scientific community for
essentially the same reasons we noted that this conclusion needed
support either in scientific testing or through validation by peer
review or publication.

                                   B.

   We grant a party’s motion for summary judgment under Rule 56(c)
only if the case presents no genuine issues of material fact. Anderson
v. Liberty Lobby, Inc., 

, 247-48 (1986). The only evi-
dence the plaintiffs provided indicating that the picloram in Grace’s
fertilizer caused their cancers was the expert testimony of Dr. Levin.
Without that evidence, the plaintiffs’ case is devoid of the proximate
causation element. Thus, there is no genuine issue as to causation, and
we are of opinion the district court properly granted the defendants’
motion for summary judgment on that basis.

                                  III.

   We review a district court’s decision denying leave to amend a
complaint under Rule 15(a) for abuse of discretion. Foman v. Davis,

, 182 (1962). A district court should grant leave to
amend unless the motion was made in bad faith or after undue delay,
or with a dilatory motive, or the amendment would cause undue prej-
udice to the non-moving party, or the amendment would be futile.
Island Creek Coal Co. v. Lake Shore, Inc., 

, 279 (4th
Cir. 1987) (quoting Foman, 371 U.S. at 182). A district court should
not deny leave to amend because of mere delay. Island Creek, 832
F.2d at 279. Delay must be accompanied by prejudice, bad faith, or
futility to comprise sufficient basis for denial of leave to amend.
Island Creek, 832 F.2d at 279. Under the facts of this case, we are of
opinion that the district court did not abuse its discretion in denying
the plaintiffs leave to amend their complaints.

  The district court denied Mrs. Marsh’s 1992 motion to amend her
complaint to include 2,4-D as a cause of her cancer after finding not
10                MARSH v. W. R. GRACE & COMPANY
only that the plaintiff had unduly delayed in making the motion, but
also that granting the motion would cause prejudice to the defendants.
The court observed that the parties had engaged in extensive, continu-
ing, and expensive discovery directed to picloram. Adding another
chemical at that point in the proceedings, after defendants had filed
a motion for summary judgment, would basically force the parties to
start the discovery proceedings anew. Additionally, the court noted
that the plaintiff had known of the presence of 2,4-D since early in
the litigation and, essentially, had no justifiable reason for waiting to
file her motion to amend when the court had granted one such motion
in early 1991. Unlike the case in Island Creek, discovery here did not
progress at a desultory pace, the plaintiff did not discover the new
contaminant recently, and both parties had concentrated their discov-
ery and efforts on picloram. See Island Creek, 832 F.2d at 279-80
(finding district court abused its discretion in denying leave to amend
complaint to include a new, recently discovered basis for relief).

   The district court was also acting within its discretion when it
denied Speer’s 1994 motion to amend his complaint. The four year
delay before Speer’s motion to amend was unnecessary. The same
attorney represents all three plaintiffs, and he made an almost identi-
cal motion to amend in Mrs. Marsh’s case. The two year delay
between that motion and the one in Speer’s case is unjustifiable. All
of the facts necessary for such a motion had been available to the
attorney for over four years. Additionally, as the district court noted,
granting the motion at that time would prejudice the defendants. The
case had reached summary judgment stage and the parties had com-
pleted years of discovery that the defendants would be forced to
repeat if the court allowed a new causal chemical into the case. It
appears that the plaintiffs’ amendment was no more than a last chance
attempt to ward off summary judgment, which is not well taken. Cf.
Sandcrest Outpatient Servs., P.A. v. Cumberland County Hosp. Sys.,
Inc., 

, 1149 (4th Cir. 1988).

   While we acknowledge that plaintiffs should have the right to
amend their complaints freely as the ends of justice require, we are
of opinion that the facts in this case support the district court’s discre-
tionary decisions to deny amendment to the complaints.

   For the reasons expressed in the opinion of the district court, its
judgment is accordingly
                MARSH v. W. R. GRACE & COMPANY                  11
                                                     AFFIRMED.*

 *The motion that we reconsider a clerk’s order denying plaintiffs’
motion to supplement the brief is denied.