Table 4

Distribution of BRCA1 mutations by disease characteristics and family history in 645 breast cancer cases

CharacteristicsTotal testedBRCA1 MutationsPe (Fisher’s exact test)
Group 1aGroup 2bGroup 3c
n% (95% CI)dn% (95% CI)dn% (95% CI)d
Age at diagnosis
 <4525610.4 (0.01, 2.2)197.4 (4.5, 11.3)20.8 (0.09, 2.7)0.29
 ≥4538961.5 (0.6, 3.3)205.1 (3.2, 7.8)61.5 (0.6, 3.3)
 Total cases64571.1 (0.4, 2.2)396.0 (4.3, 8.2)81.2 (0.5, 2.4)
Family history of breast cancerf
 Noneg59450.8 (0.3, 2.0)396.6 (4.7, 8.9)71.2 (0.5, 2.4)0.07
 First degreeh2926.9 (0.8, 2.3)00.0 (0.0, 11.9)i13.4 (0.1, 17.8)
 Grandmother only400.0 (0.0, 60.2)i00.0 (0.0, 60.2)i00.0 (0.0, 60.2)i
 Relative had breast cancer <45 yrsj10110.0 (0.2, 4.4)00.0 (0.0, 30.8)i10.0 (0.2, 4.4)0.22
 Relative had breast cancer ≥45 yrs2214.5 (0.1, 22.8)00.0 (0.0, 15.4)i00.0 (0.0, 15.4)i
Family history of ovarian cancerf
 Noneg62361.0 (0.4, 2.1)396.3 (4.5, 8.4)81.3 (0.6, 2.5)0.07
 Yes (mother)4125.0 (0.6, 80.6)00.0 (0.0, 60.2)i00.0 (0.0, 60.2)i
Family history of breast or ovarian cancerf
 Nog59040.7 (0.2, 1.7)396.6 (4.7, 8.9)71.2 (0.5, 2.4)0.004
 Yes3738.1 (1.7, 21.9)00.0 (0.0, 9.5)i12.7 (0.07, 14.2)
  • a Frameshift and splice-site mutations (no nonsense changes were found in this study).

  • b Missense changes, single amino-acid deletions and intronic changes ≤40 bases from coding region.

  • c Silent changes, intronic changes >40 bases from coding region, and changes after the BRCA2 polymorphic stop codon at amino acid 3326.

  • d 95% confidence interval (CI) for proportion of cases with mutations in this group.

  • e P for differences in mutation frequencies among women in different categories of each characteristic.

  • f Family history of cancer was unknown for 18 women; there were no BRCA1 mutations among these women.

  • g Includes 112 women with no family history of cancer in first-degree female relatives, but history was incomplete for one or both grandmothers; also includes 4 women with no family history of cancer in either grandmother, but history was incomplete for one or more first-degree female relatives.

  • h One woman also had family history of breast cancer in maternal grandmother.

  • i One-sided 97.5% confidence interval.

  • j Relative’s age at breast cancer was unknown for 1 woman.