Survival Implications Associated with Variation in Mastectomy Rates for Early-Staged Breast Cancer

Table 2

Estimates of the effect of mastectomy relative to breast conserving surgery with radiation on 7-year survival by estimator and sample subsets¹.

			Estimator
Estimation Sample	𝑁	Mastectomy percentage	Linear probability estimates^2	Instrumental variable estimates^3
		(1st–5th quintile range)	Mastectomy effect on 7-year survival (std. error)	Instrument chow test [44] 𝐹-value	Over; identification test 𝐹-value	Mastectomy effect on 7-year survival (std. error)
Full sample	28,675	56.2	−0.030^∗	264.01^∗	0.60	−0.071^∗
		(37.9–68.6)	(0.006)			(0.029)
Trial status comparable^4
Yes	5,003	43.5	−0.001	50.43^*	0.57	0.05
		(25.5–57.0)	(0.010)			(0.05)
No	23,672	58.8	−0.037^∗	215.60^*	0.38	−0.10^∗
		(40.4–71.1)	(0.006)			(0.03)
Stage
Stage I	17,908	47.3	−0.017^∗	174.75^*	0.93	−0.02
		(28.2–61.3)	(0.006)			(0.03)
Stage IIa	7,700	67.2	−0.049^∗	63.02^*	1.28	−0.15^∗
		(50.3–78.5)	(0.011)			(0.06)
Stage IIb	2,827	80.2	−0.085^∗	23.81^*	2.03	−0.22
		(66.4–88.7)	(0.023)			(0.13)
Age
66–70	8,037	50.9	−0.010	75.53^*	1.99	0.02
		(33.5–64.3)	(0.009)			(0.05)
71–75	8,405	51.4	−0.016	81.82^*	0.15	−0.05
		(31.4–64.1)	(0.010)			(0.05)
76–80	6,611	57.5	−0.049^∗	69.94^*	0.42	−0.11
		(39.9–71.2)	(0.012)			(0.06)
81+	5,622	69.2	−0.065^∗	37.15^*	1.06	−0.19^∗
		(52.3–78.6)	(0.015)			(0.09)

¹All models also specified all measured covariates listed in the variable definition section and are more fully described in Keating et al. [8].
²Average treatment effect on the treated (ATT). In this case, average effect of mastectomy on 7-year survival for those patients choosing mastectomy.
³Local average treatment effect (LATE). The average effect of mastectomy on 7-year survival for those patients whose mastectomy choice would have changed with local area mastectomy practice style.
⁴ESBC patients with low-risk tumors (stage I), little comorbid illness, and age ≤ 70.
^∗𝑃<0.05.