According to the World Health Organization (WHO), cancer is one of the leading causes of morbidity and mortality in the world, with 8.8 million deaths reported in 2015.¹ Lymphomas are a type of hematological malignancy with highly variable immunophenotypes, clinical and histological features and genetic abnormalities.² They are classified into two groups: Hodgkin's lymphoma (HL) and non-Hodgkin's lymphoma (NHL),³ and about 500 000 diagnoses of NHL are made worldwide every year.⁴

As per the 2018 report by the Global Cancer Observatory (GCO), NHL had an incidence of 2.8% with 1 353 273 cases over a 5-year period (2013-2018), while HL had an incidence of 0.44% with 275 947 cases over a 5-year period (2013-2018).⁵ In Colombia, as reported by the Fondo Colombiano de Enfermedades de Alto Costo (High Cost Diseases Fund), 7 507 and 1 770 patients over the age of 18 were diagnosed with NHL and HL, respectively, between 2015 and 2016.⁶

Although the clinical presentation of both types of lymphoma is similar, prognosis varies according to the subtype.⁷ In NHL patients, the relative survival rate is 70% and 60% at 5 and 10 years, respectively,⁸ while survival in HL patients depends on the stage of the disease: the relative 5-year survival rate is 90% for stages I and II, 80% for stage III, and about 65% for stage IV.^9,10 Advances in clinical and therapeutic management of patients with lymphoma, such as autologous and allogeneic stem cell transplants, improve progression-free survival in this disease.^11,12

Even though lymphoma patients have specific concerns that generate physical, social, psychological, and functional deterioration,¹³ to date, in Colombia there are no valid instruments that allow assessing health-related quality of life in this population. Quality of life is considered an outcome of cancer treatment and is used as a measure of well-being in patients with this disease.¹⁴ The WHO describes quality of life as "an individual's perception of their position in life in the context of the culture and value systems in which they live and in relation to their goals, expectations, standards and concerns."^15,p3 To assess an individual's quality of life, it is necessary to take into account their subjective perceptions of health, their emotional response to the different situations they face, as well as their level of job satisfaction, their interpersonal relationships and their life purpose.¹⁶ With this in mind, the concept of quality of life allows us to obtain information about the impact of the disease and its treatment on both the physical and emotional aspects of patients' lives.

According to the American Society of Clinical Oncology,¹⁷ quality of life should be considered a priority outcome of treatment in oncology patients. Therefore, it should be considered for the development of clinical practice guidelines and the evaluation of new technologies for therapeutic purposes.

The scales suggested to measure quality of life in cancer patients include the European Organisation for Research and Treatment of Cancer (EORTC) quality of life questionnaire (EORTC QLQ-C30),¹⁸ which is the most widely used instrument in this population,¹⁹ and the Quality of Life Patient/Cancer Survivor Version (QOL-CSV) scale, designed based on an instrument to evaluate pain management in cancer patients.^20,21 On the other hand, the 36-Item Short Form Health Survey (SF-36), elaborated in the United States, seeks to evaluate the positive and negative states of health, and their Implications in the quality of life of patients with different types of diseases.^22,23

One of the few scales that measure quality of life in patients with lymphoma is the Functional Assessment of Cancer Therapy - Lymphoma (FACT-Lym) scale, developed by the Functional Assessment of Chronic Illness Therapy (FACIT) organization in 2005.²⁴ The literature reports on the original validation, carried out in 2013, and the validation carried out the same year in Greece;²⁵ however, the latter is partial as it does not take into account all the clinimetric properties of the instrument. The FACT-Lym scale is made up of the items included the generic module of the FACT-G scale^26,27 and by 15 specific items for physical and emotional symptoms of patients with lymphoma. These scales have been designed to be used both in clinical interviews and for self-administration.²⁸

Due to the importance of evaluating quality of life in patients with lymphomas and the unavailability of adequately validated instruments to do so in Colombia, the objective of this study was to establish the clinimetric properties of the FACT-Lym scale in Colombian patients with lymphoma.

A validation study of scales following the classical test theory was carried out using the FACT-Lym questionnaire. Authorization from the FACIT organization, which was in charge of translating the scale into Spanish, was obtained before beginning with the study. The owners of this instrument do not authorize making new adaptations in Spanish since they already have one in this language, so no cross-cultural adaptation was required.

The sample was selected by convenience and 301 patients who met the following inclusion criteria were included: being >18 years old, verbally agreeing to participate, having a diagnosis of lymphoma at any stage confirmed by histology with or without treatment, and being treated at the Instituto Nacional de Cancerología (National Cancer Institute) between 2016 and 2018 in outpatient, inpatient, or emergency services. Patients with cognitive or sensory impairments that prevent understanding the questionnaire were excluded.

To estimate sample size, the PASS® program was used and all the components of the scale validation process were considered. The exploratory and confirmatory factor analysis was performed on a sample of 301 patients, taking into account the recommendation of MacCallum & Hong²⁹ of having at least 300 sample observations, using the PASS® program and including all the components of the scale validation process. To estimate concurrent validity, a sample size of 163 patients was calculated considering a Pearson's correlation coefficient of 0.2 for the null hypothesis (Ho) and 0.4 for the alternative hypothesis (Ha). To estimate the reliability of the instrument, and using the test-retest method, a sample size of 64 patients was defined, assuming a Lin correlation coefficient of agreement of 0.6 and 0.7 for Ho and Ha, respectively. ^30,31 To estimate the internal consistency of the scale, a sample size of 85 patients was established, taking Cronbach's alpha coefficient values of 0.5 and 0.7 for Ho and Ha, respectively, and bearing in mind that the FACT-Lym scale has 15 items.^32,33 Finally, in the sensitivity analysis, sensitivity to change was determined based on information from the study conducted by Hlubocky etal.,²⁴ in which, an effect size of -0.87 on the overall score of the FACT-Lym subscale was observed with sample sizes of at least 14 patients.

As for the sociodemographic variables, the average age was 56.7 years (SD=16.4 years), 54.82% were women and 61.4% were classified in the socioeconomic strata 1 and 2 (Table 1). It should be noted that in Colombia, socioeconomic status is classified into strata that range between 1 and 6, being 1 the lowest and 6 the highest (Table 2).

Table 1

Variables		n	%
Sex	Female	165	54.82
	Male	136	45.18
Marital status	Single	73	24.5
	Common-law marriage	73	24.25
	Married	104	34.55
	Divorced	20	6.64
	Widower	31	10.30
Socioeconomic Stratum	1	73	24.25
	2	112	37.21
	3	100	33.22
	4	15	4.98
	No data	1	0.33
Occupation	Home	92	30.56
	Unemployed	66	21.93
	Freelancer	53	17.6
	Employed	48	15.95
	Retired	34	11.30
	Student	8	2.66
Place of origin	Bogotá D.C.	174	57.81
	Cundinamarca	47	15.61
	Boyacá	28	9.3
	Tolima	20	6.64
	Atlantic Coast	11	3.65
	Eastern Plains and Amazon	12	3.98
	Other	9	2.99

Source: Own elaboration.

Table 2

Stratum	Description
1	Low-low. Beneficiaries of home utility subsidies.
2	Low. Beneficiaries of home utility subsidies.
3	Middle-low. Beneficiaries of home utility subsidies.
4	Middle. They are not beneficiaries of subsidies, nor do they pay surcharges; they pay exactly the amount that the company defines as the cost for providing home utilities.
5	Middle-high. They pay surcharges (contribution) on the value of home utilities.
6	High. They pay surcharges (contribution) on the value of home utilities.

Source: Elaboration based on the data issued by National Administrative Department of Statistics.⁴¹

With respect to the clinical variables, 256 patients (85%) were diagnosed with NHL and 45 with HL (14.9%). 19.6% of patients were in stage IVb of the disease, 16% in stage IV, 9% in stage IIIb, 7.67% in stage IIb, and 4% in stage I. Of the total amount of patients, 270 (90%) had received chemotherapy; 47 (15.6%), biological therapy; 22 (7.33%), palliative care; and 19 (6.33%), autologous transplant.

Health-related quality of life is a concept used to measure the general well-being of patients, which makes it necessary to have valid and reliable instruments to assess the psychosocial aspects of an individual and their influence on health status. Therefore, the FACT-Lym scale was validated in this study to evaluate quality of life in lymphoma patients since it had not been previously done in Colombia.

Most patients included in this study were women, which coincides with the data presented by the Fondo Colombiano de Enfermedades de Alto Costo,⁶ which reports that the majority of lymphoma cases in the adult Colombian population occur in women. In terms of the clinical characteristics of the patients included, most were in advanced stages of the disease and had received chemotherapy. The most frequent subtype was NHL, which coincides with the data reported by the Global Cancer Observatory.⁵

Regarding the results obtained in the items of the scale, it has been suggested that the items: "I feel pain in certain parts of my body", "I have trouble sleeping at night", "I get tired easily", "I am worried about getting infections" and "I am concerned about developing new symptoms associated with the disease" may be associated with a lower quality of life in patients and, consequently, represent an important marker of quality of life in this population since the medians obtained for these items were low. However, further studies should be conducted using other methods, such as the Rasch model, to test this hypothesis.

The exploratory factor analysis showed that the FACT-Lym subscale has a simple structure consistent with the FACT-G scale; this analysis allowed establishing two domains: physical condition and specific concerns. Moreover, since the factor loading values were adequate and the uniqueness values were within the recommended ranges, it was concluded that all items in the FACT-Lym subscale are appropriately represented in the factorial structure, suggesting that there were no maladjusted or redundant items in the specific component of the scale.

In terms of internal consistency, the results obtained for the total scale and for each of the items indicated that the FACT-Lym scale has adequate reliability, a result that is consistent with the study by Hlubocky et al.,²⁴ who reported alphas between 0.90, 0.93, and 0.95 on this subscale. With respect to sensitivity to change, no statistically significant differences were observed between the results before and after treatment; however, the differences found in the two measurement moments were very little, and no changes were observed in the other subscales of the FACT-G scale, an instrument that has already been validated and that has adequate sensitivity to change; therefore, it was concluded that the lack of differences is explained by the stability of the construct and not by a clinimetric defect of the scale

Finally, most of the patients included in the study had a low socioeconomic level. This could be a selection bias of the study because perceptions or interpretations related to the socioeconomic situation may have been excluded.

The validation of the FACT-Lym scale in Colombia showed that it has a consistent factorial structure and adequate reliability. However, its sensitivity to change must be confirmed by evaluating the scale's performance in other populations.