Number needed to treat and associated incremental costs of treatment with enzalutamide versus abiraterone acetate plus prednisone in chemotherapy-naïve patients with metastatic castration-resistant prostate cancer

Figures & data

Table 1. Input data for drug costs, monitoring, and efficacy.

Input	ENZA	AA
Drug cost
Daily dose	160 mg^6	1000 mg + prednisone 10 mg^7
WAC per mg, USD	$1.84^19	$0.29, $0.06 (prednisone)^19
Proportion of patients with concomitant prednisone use, %	27^6	100^7
Compliance rate (Astellas internal data), %	92	91
Mean treatment duration within 1 year, months*	9.6^6	9.0^7
Monitoring
Physician visit (CPT: 99213)	$72.94 × once monthly^20	$72.94 × once monthly^7^,^20
Basic metabolic panel test (CPT: 80048)	0^6	$15.55 × once monthly^7^,^21
Hepatic function panel test (CPT: 80076)	0^6	$15.02 × once monthly^7^,^21
1-year efficacy
rPFS rate, %	65.0^6	58.0^7
Mean rPFS duration, months^†	10.2^6	9.6^7
Chemotherapy-free rate, %	83.4^3	79.6^17
Mean chemotherapy-free duration, months^†	11.3^3	11.1^17
Overall survival rate, %	91.8^6	90.7^7
Mean overall survival duration, months^†	11.7^6	11.6^7

AA, abiraterone acetate plus prednisone; CPT, current procedural terminology; ENZA, enzalutamide; rPFS, radiographic progression-free survival; USD, United States Dollars; WAC, wholesale acquisition cost.

* Mean treatment durations were estimated using the area-under-the-curve technique based on the reported median treatment durations and constant hazard of discontinuation assumption.

^† Durations with clinically meaningful outcomes were calculated using the area-under-the-curve technique based on the respective Kaplan-Meier curves.

Table 2. Input data for adverse events.

Adverse event	Unit cost, USD	1-year rates of Grade 3/4 adverse event*, %
		ENZA^3^,^6	AA^7^,^22
Acute renal failure^20^,^24^†	$9,958	1.0	–
Adrenocortical insufficiency^20^,^24^†	$9,533	–	0.4
Asthenia/fatigue^25^,^27	$8,419	2.3	1.9
ALT increased^20^,^24^†	$6,110	0.2	5.3
AST increased^20^,^24^†	$6,110	–	2.7
Atrial fibrillation^30	$17,098	0.2	1.6
Back pain^20^,^24^†	$7,026	1.7	–
Cardiac events^26	$20,241	1.7	6.6
Dyspnea^25^,^27	$10,863	0.4	2.1
Edema^20^,^24^†	$7,397	0.1	0.3
Fall^37	$10,752	1.1	–
Hematuria^20^,^24^†	$7,577	0.9	1.1
Hyperglycemia^23	$2,505	–	5.6
Hypertension^25	$2,284	5.0	3.4
Hypokalemia^20^,^24^†	$6,342	–	2.4
Joint swelling^20^,^24^,^†	$6,986	1.1	1.8
Lower respiratory tract infection^38	$5,211	1.0	–
Lymphopenia^25	$11,668	–	7.5
Non-pathological fracture^29	$4,229	1.4	–
PRES^20^,^24^†	$13,678	0.1	–
Seizure^28	$8,855	0.1	–

AA, abiraterone acetate plus prednisone; ALT, alanine aminotransferase; AST, aspartate aminotransferase; ENZA, enzalutamide; PRES, posterior reversible encephalopathy syndrome; USD, United States Dollars.

* The adverse event rates for enzalutamide and abiraterone acetate plus prednisone were obtained by prorating the rates reported in the trials by the median treatment duration to a 1-year rate, except for PRES, which was based on assumption.

^† Due to lack of relevant information, it was assumed that costs for treating Grade 3/4 events would be equivalent to a hospital stay with relevant condition and a follow-up outpatient visit.

Table 3. Input data for post-progression and end-of-life costs.

Inputs	Value
ENZA: proportion of patients receiving each post-progression treatment^3^*, %
Sipuleucel-T	2.2
Docetaxel	53.3
ENZA	0.0
AA plus prednisone	35.0
Cabazitaxel	9.5
AA: proportion of patients receiving each post-progression treatment^22^*, %
Sipuleucel-T	7.4
Docetaxel	50.8
ENZA	25.5
AA plus prednisone	0.0
Cabazitaxel	16.3
Costs for post-progression treatments, USD
Sipuleucel-T cost of one treatment course	$121,479^19^,^31
Docetaxel monthly cost	$1,317^19^,^32^,^39
ENZA monthly cost	$8,848^6^,^19
AA monthly cost	$8,646^7^,^19
Cabazitaxel monthly cost	$13,391^19^,^33
Hospitalization due to progression or death, USD
One-time hospitalization cost	$13,407^24
Hospice care
Proportion of patients receiving hospice care before death, %	53^40
Average length of stay in hospice, days	47^40
Cost per day in hospice, USD	$171^41

AA, abiraterone acetate plus prednisone; ENZA, enzalutamide; USD, United States Dollars.

* Proportions of patients receiving each post-progression treatment were derived from the proportions reported in the trials and reweighted to 100%, assuming that each patient would only receive one type of post-progression treatment, other than the original therapy, within the time horizon.

Figure 1. Illustration of methodology. NNT, number needed to treat; rPFS, radiographic progression-free survival.

Table 4. Total cost per treated patient within a 1-year time horizon.

Cost component	ENZA, USD	AA, USD	Difference (ENZA–AA), USD
Drug cost	$77,791	$70,911	$6,880
Monitoring cost	$697	$933	−$236
Adverse-event-related cost	$1,361	$4,011	−$2,650
Post-progression cost	$13,142	$19,608	−$6,465
End-of-life cost	$1,449	$1,643	−$194
Total cost per treated patient	$94,440	$97,105	−$2,666

AA, abiraterone acetate plus prednisone; ENZA, enzalutamide; USD, United States Dollars.

Table 5. Clinical outcomes and associated costs comparing ENZA with AA within a 1-year time horizon.

Outcome	NNT	Cost difference, USD	Incremental cost per additional patient with outcome
Free of progression or death  (based on rPFS)	14	−$2,666	Dominant
Chemotherapy delayed  (based on chemotherapy-free rate)	26		Dominant
Death avoided  (based on overall survival)	91		Dominant

AA, abiraterone acetate plus prednisone; ENZA, enzalutamide; NNT, number needed to treat; rPFS, radiographic progression-free survival; USD, United States Dollars.

Figure 2. One-way sensitivity analysis.

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