In addition to the sexual function scales, several of the reviewed articles reported using functional status or quality of life measures that include one or more items related to sexual function. For example, the Functional Assessment of Cancer Therapy-Breast Scale (FACT-B) [35
] assesses sexual function in its subscale about additional concerns, the Cancer Rehabilitation and Evaluation System Short Form (CARES-SF) contains a sexual function subscale [36
], and the Psychosocial Adjustment to Illness Scale (PAIS) includes a subscale of sexual dysfunction and quality of dyadic relationship [37
]. Likewise, several of the site-specific measures of the European Organization for Research and Treatment of Cancer quality of life questionnaires (EORTC QLQ) contain function or symptom subscales to assess sexual function or dysfunction, such as the EORTC QLQ Colorectal-38, the EORTC QLQ Breast-23, the EORTC QLQ Ovarian-28, and the EORTC QLQ Head & Neck-35 [40
]. Additionally, Gotay and her colleagues [41
], after conducting qualitative research with cancer survivors, added sexuality/intimacy items to the European Organization for Research and Treatment of Cancer Quality of Life Questionnaire – Cancer 30 (EORTC QLQ-C30).
Dimensionality and Domains
Only a few measures were purposively constructed to be unidimensional, the majority being multidimensional. Exploratory factor analysis or principal components analysis were the most common statistical methods used to identify or verify subdomains. No psychometric reports indicated the use of confirmatory factor analysis or item response theory.
Almost all measures included domains related to stages of the sexual response cycle as defined by Masters and Johnson [42
], including excitement/arousal, plateau/continued arousal and orgasm, although the specific content varied considerably between measures. The most common domains and the number of measures (#) identifying these domains were:
- Sexual arousal (lubrication, erectile (dys)function) (19)
- Sexual (dis)satisfaction (16)
- Sexual desire (interest, drive, avoidance, receptivity, nonsensuality) (15)
- Sexual pleasure (orgasm) (12)
- Frequency of sexual activity (12)
- Problems affecting sexual function (anorgasmia, pain, vaginismus) (5)
Less common domains (or constructs) related to cognitive aspects, including sexual thoughts or fantasies, sexual self-esteem, sexual self-image, sexual self-reflection, psychosexual stimulation, emotional goals, and broader cognitive dimensions such as sexual attitudes and beliefs, motivation, values, and expectations. The most infrequent domains were sexual role, partner function or perceptions, nonsexual interactions or communication, relationship satisfaction, and health-specific sexual dysfunction. Our preliminary conceptual model, based on the sorting of the measures’ reported domains, contains five domains: Sexual Response, Intrapersonal, Interpersonal, Frequency, and Overall Satisfaction.
Our literature review highlights the wide array of sexual function measures administered to cancer populations. Although we focused exclusively on the cancer literature, our findings approximate those of other reviews that examined the domains and psychometric properties of sexual function instruments used with general and medically ill populations. The first review by Arrington et al. [21
] identified 45 sexual function-specific measures and 12 global measures, and concluded that while there is no consensus on sexual function domains, the most common domains were excitement/arousal, interest/desire, satisfaction/quality, and performance. The second review by Corona et al. [18
] identified 30 patient self-report measures of sexual function published in their entirety between 1969 and 2005, 22 measures for males and/or males and females, 8 measures for females only. Our secondary review of these 30 measures found 83 unique domains, the most common relating to psychological constructs (e.g., emotional responses to sexual problems, sexual concerns), sexual desire/interest, sexual partner or relationship, and overall sexual satisfaction or pleasure. These domains are consistent with our preliminary conceptual model which is expected to undergo revision after further qualitative and quantitative testing.
For measures of male sexual function, there appears to be complete accord for including erectile function as a domain. For measures of female sexual function, sexual interest or desire, and ability to reach orgasm are the most common domains. In contrast, there appears to be no consensus among measures for both males and females with respect to domains related to non-genital activity, affection behaviors, or sexual intimacy, and, rarely, partner sexual function, sexual attractiveness or body-image, or sexually-related cognitive or emotional dimensions. Others recommend that these latter domains be classified as secondary or mediating dimensions [20
Most of the identified measures were gender-specific, consistent with other reviews of general sex measures [18
]. For specific research applications, such as evaluating interventions to treat erectile dysfunction, the use of gender-specific measures is clear. In other settings, however, it may be desirable to assess the degree of sexual issues independent of gender. For example, describing the burden of sexual difficulties in long-term survivors would benefit from assessing men and women on comparable metrics where possible. Generating gender-neutral assessments is challenging and likely will require a modular approach to measure development.
From our review, only the UCLA PCI/EPIC, IIEF, and FSFI immerged as “legacy” measures, that is, measures with extensive psychometric testing and sufficient clinical administration in oncology settings to help set the standard for the development of subsequent sexual function measures intended for use with cancer survivors. Indeed, in the last 15 years the UCLA PCI/EPIC and the IIEF have been used in about two-thirds of studies that examine the sexual function of individuals treated for cancer. While both are reliable and valid indicators of male sexual function, there are important differences between these measures. The 20-item UCLA PCI was originally developed for use with the Rand 36-item Health Survey (SF-36) to yield a comprehensive quality of life assessment of men with prostate cancer [46
]; the IIEF was developed with support from a pharmaceutical company for the purpose of evaluating multinational clinical trials of sildenafil citrate [47
]. Another distinction is that the UCLA PCI and its 26-item and 50-item EPIC versions specifically target symptoms associated with prostate cancer compared to the IIEF which assesses sexual function only. Also, the UCLA PCI has been shown to discriminate between older men with and without prostate cancer [26
], and has been successfully used in large prospective studies of prostate cancer conducted in the U.S. [e.g., 48
]. The discriminant validity of the IIEF between men with and without cancer has not been reported, but the measure is able to discriminate between men receiving and not receiving sildenafil citrate for erectile dysfunction after radical prostatectomy, (e.g., 51
], and between men receiving or not receiving tadalafil after radiation therapy for prostate cancer [15
]. Given their comparable levels of reliability and validity and use with cancer populations, decisions to use one or the other measure depend on research or clinical objectives as well as practical considerations. Measures that produce multiple conceptually precise subscales (e.g., EPIC) might be better suited for research purposes because of the need to detect subtle intergroup differences over time, whereas measures with fewer, more global dimensions (e.g., IIEF-5) might be adequate for clinical purposes (i.e., for screening to help identify who may be having problems, or as a catalyst to begin patient-provider communication about sexual function). Too, since both the UCLA/EPIC and IIEF are available at no cost, clinical use may favor the IIEF which takes about 5 – 10 minutes to self-administer while compared to the 20-30 minutes needed for the UCLA/EPIC versions. It should be noted that the male version of the CaPS SF will capture and test similar domains and items from both measures (in addition to those from other measures) with the goal of producing targeted, clinically relevant outcomes with the least possible administration and response burdens for all cancer sites.
Among the identified measures of female sexual function used in oncology, only one measure appears to be emerging as a legacy measure, namely the FSFI which was developed by the IIEF originator, again with the support of pharmaceutical funding [30
]. Used in studies of urologic [54
], gynecologic [55
], breast [60
], and rectal cancer survivors [62
], it appears to have undergone extensive psychometric testing, and is able to discriminate between clinical and non-clinical populations [64
]. The 19-item FSFI takes less than 15 minutes to complete, uses a 4-week recall period, and is available at no cost [30
]. This measure has been used in clinical trials of sildenafil citrate [65
] and vardenafil [67
] to evaluate female partner satisfaction, and thus might be a particularly useful measure in studies of male cancers where partner assessments are included as an outcome. The use of the FSFI in studies of female cancer survivors also appears to be growing as indicated by reports published subsequent to our CaPS-SF literature review [e.g., 68
]. The extent to which the FSFI is used in clinical settings to help evaluate and treat the sexual function of female cancer survivors is unknown. Our female CaPS SF measure will capture and test similar domains and items as found in the FSFI.
Unexpectedly, our literature review indicates that sildenafil citrate, approved by the U. S. Food and Drug Administration in 1998 to treat erectile dysfunction, paved the way for sexual function measures to be used in oncology. As a consequence, among cancer populations, the assessment of male sexual function has far outpaced the assessment of female sexual function, an unanticipated finding given decades of research documenting compromised sexual function after treatment for gynecologic and breast cancer. Although several well-established measures of female sexual function are available (e.g., Derogatis Sexual Functioning Inventory, Brief Index of Sexual Function for Women, Female Sexual Function Index), it was also surprising that they have not been used as extensively as the UCLA-PCI or IIEF.
A significant limitation of the existing measures is the lack of data demonstrating the validity of the measures for different cancer sites and across the continuum of cancer care, a limitation that presents challenges for conducting meaningful cross-study comparisons across all cancer sites. As indicated above, important exceptions are the UCLA PCI and the IIEF both of which have been used post-diagnosis through long-term follow-up care.