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Years of potential life lost: Another indicator of the impact of cutaneous malignant melanoma on society
Years of potential life lost: Another indicator of the impact of cutaneous malignant melanoma on society Vicki A. Albert, BA, Howard K. Koh, MD, FACP,* Alan C. Geller, RN, MPH, Donald R. Miller, SeD, Marianne N. Prout, MD, MPH, and Robert A. Lew, PhD
Boston, Massachusetts Years of potential lifelost (YPLL) is an indicatorof premature mortalitythat complements traditional incidence and mortality rates and that facilitates comparisons among different cancers. We calculated YPLL from cutaneousmelanomaand 11 other cancersroutinelyrecorded and tracked by Surveillance, Epidemiology and End Results (SEER). YPLL from cutaneous melanoma ranked eighth for persons youngerthan 65 yearsof age and fourth for those 20 to 49 years of age. An averageof 17.1 YPLL per death were due to melanoma, one of the highest rates for adult-onset cancers.The resultsof our study, the first to apply YPLL to cutaneous melanoma, emphasize the disproportionate impact of this canceron youngand middle-aged adults and reemphasize the importance of this cancer as a public health priority. (J AM ACAD DERMATOL 1990;23:308-10.)
In 1990 cutaneous melanoma will strike 27,000 people, account for 5800 deaths,' and be responsible for the premature loss of numerous lives in the United States. The rate of increase in the incidence of cutaneous melanoma is projected to soon surpass that for virtually all other malignancies.e? As the incidence of cutaneous melanoma has risen, so has the mortality rate. Data from Surveillance, Epidemiology, and End Results (SEER)6 show that in 1981 the mortality rate for cutaneous melanoma was 2.0 per 100,000 population, up from 1.6 per 100,000 in 1973. SEER data also show that the mortality rate for melanoma ranks third among cancers in men and women 25 to 29 years of age and also ranks highly in the group 20 to 50 years of age. Overall mortality rates, however, do not reflect the ages at which persons die. Years of potential life lost (YFLL) is a simple measure that accounts for age at death together with the absolute number of deaths; it therefore indicates premature mortality.
From the Departments of Dermatology and Medicine, Boston University School of Medicine, and Section of Epidemiology and Biostatistics, Boston University School of Public Health. Sponsored in part by NCI grant IK07-CAOI38Q.Ol. Reprint requests: Howard K. Koh, MD, Boston University School of Medicine, 80 E. Concord St. C-321, Boston, MA 02118. "'Recipient of the Preventive Oncology Academic Award from the National Cancer Institute. 16jl/17Ci08
308
We applied this measure to cutaneous melanoma to demonstrate the disproportionately high impact of this cancer on young and middle-aged adults. METHODS
We used data obtained from Cancer Incidence and Mortality in the United States." SEER 1973 to 1981,to calculate YPLL beforeage 65 years for the 12 cancers that mostcommonly causedeath. Thesecancersand others are routinely recorded and tracked by SEER. The 1980 U.S. census population was used as the reference population.iThe numberof cause-specific deaths in each age intervalwas calculated by multiplying the mortality rate for each cancer by the sizeof the 1980U.S. population in each age interval. YPLL was defined as the summation of the number of cause-specific deaths occurring in 5-yearage intervals(beginning at birth) multiplied by the number of years remaining betweenthe midpoint of each 5-year age interval and the cutoff age of 65 years. YPLL per death was alsoderived for each cancer.
RESULTS YPLL and deaths for Americans up to 65 years of age resulting from the 12 cancers studied are shown in Table I. Cancers are presented in descending order of rank for YPLL per cancer death. Information on YPLL per death rank is followed by YPLL per death, YPLL rank, number of YPLL, and percentage of total YPLL; and rank, number, and percentage of deaths for each cancer. Mortality from cutaneous melanoma ranked elev-
Volume 23 Number 2, Part 1 August 1990
Years ofpotential life lost 309
Table I. Relative impact of 12 cancers in persons younger than 65 years in the United States (1980): YPLL rank, death rank, and YPLL per death Cancer site
RankoCYPLL per death
No.ofYFLL per death
1 2 3 4 5 6 7 8 9 10
2I.l 17.1 15.2 12.2 10.9 10.0 9.6 9.5 9.1 8.8 8.8 8.6
Adult leukemia" Melanoma"
Cervix" Breast Ovary Stomach Pharynx and larynx Colon Lung (non-small cell) Pancreas Esophagus Lung (small cell)
11
12
No. of deaths(%)
No.oC
YPLL(%)
6 8 9 2 7
10 11 3 1 5 13 4
55,882 48,131 43,730 217,625 53,745 43,372 34,706 117,356 333,258 60,229 31,810 66,377
(4.5) (3.9) (3.5) (I8) (4.4) (3.5) (2.8) (9.5) (27) (4.9) (2.6) (5.4)
12
11 10 2 6 7 8 3 1 5
9 4
2,649 2,816 2,885 17,799 4,922 4,349 3,633 12,386 36,701 6,815 3,605 7,704
(2.2) (2.4) (2.4) (15) (4.1) (3.7) (3.1) (10.4) (31) (5.7) (3.0) (6.5)
*YPLL rank is higher than death rank.
enth among the cancers and was responsible for 2.4% of the total number of cancer deaths. Cutaneousmelanoma accounted for 48,131 YPLL, or 3.9% of the total YPLL, and ranked eighth for YPLL of the 12 cancers. Cutaneous melanoma, however, was the second highestranking cancer on thelist in terms of YPLL per death, accounting for 17.1 YPLL per death (see Table I). The top five ranking cancers in terms of both mortality and YPLL in Table I head the list because of the sheer number of people who die from these cancers. Except for breast cancer, mortality from these cancers occurs largely after the fifth or sixth decade oflife, with YPLL per death lessthan 10. For the cancersranked sixththrough ninth bymortality, mortality was higher than YPLL in terms of percentage and ranking. However,melanomajoins two other cancers, adult leukemia and cervicalcancer, to rank higher in YPLL than in number of deaths, reflecting increased mortality earlier in adult life and at least 15 YPLL per death. DISCUSSION
YPLL, a measure of premature mortality, complementstraditionalmortality measuresby accounting for the age at whichdeath occurred. Becauseone of the primary goals of public health is to prevent premature mortality, the Centers for Disease Control has routinely calculated and tracked YPLL for the 15 major causesof death since 1979.7,8 In many ways such YPLL analyses reflectthe impact of disease in terms of human cost better than crude incidence and mortality data. They have been used for setting national priorities for cancer control, estab-
lishing guidelines in resource allocation, and monitoring the effectiveness of screening, treatment, and other health interventions"!" Although others18. 19 have applied YPLL to cancer in foreign countries, and YPLL measurements for cancer in the United States have been published in tabular form,2o our study is the firstto apply YPLL specifically to cutaneous melanoma. The results of our study emphasize the unfortunate impact of cutaneous melanoma on young and middle-aged adults. As with adult leukemia and cervical cancer, and in contrast to most other common cancers, mortality from melanoma tends to increase relatively early in adult life, resulting in disproportionately high premature cancer mortality and a relatively high toll in YPLL. For each death from melanoma,more than 17years of potential life before age 65 years are lost, second only to adult leukemia. Melanoma will undoubtedly advance in the ranking.The dramatic increase in incidence with the rise in mortality for cutaneous melanoma will increase YPLL; moreover, in contrast to many other cancers, age-specific increases in the incidence of cutaneous melanoma have been more pronounced in the middle-aged population compared with the older age groups.i' Monitoring this trend may be important for future planning and evaluation of health initiatives. 22 Most studies measuring YPLL, including those done by the Centers for Disease Control,8,23 use a cutoff age of 65 years for the calculations. Some researchers argue that age 70 or even 75 years would better represent the public health goal of postpone-
310 Albert et al. ment of death.24. 25 We agree with Wise et a1.,9 however, who studied YPLL in three different age rangesand recommended the cutoffage of 65 years. Wise et al. noted that 65 years is the traditional retirement age and is more effective in differentiating the leading causes of premature mortality from those affecting the entire population. Indicative ofthehighriskofmelanomainyounger persons is that, amongthe 12 cancerslisted inTable I, melanoma hasthe highestincidence in persons 20 to 24 yearsof age. 2 An excess of premature mortality argues for added efforts toward screening programs for the earlydetection of a particular cancer. Cutaneous melanoma is an appropriate cancer for screening because expensive testsand procedures for its early detection are not required and because an efficient, noninvasive examination of the skin followed by appropriate excision shouldpreventmetastatic disease and reduce mortality.26 In summary, our analysis shows that cutaneous melanoma makes a disproportionately high contributionto prematurecancermortalityand causes loss of many potentially productive years of life among young and middle-aged people. We believe melanoma should be further targeted as a publichealth priorityso that steps can be taken to prevent unnecessary death and suffering. Weare grateful to Cynthia Barber for her careful review of this manuscript, to Mary Beth Mercer for her assistance in this project, and to Dr. Claudia Arrigg for unending encouragement and support.
REFERENCES I. Cancer facts lind figures. New York: American Cancer Society, 1989. 2. Greenwald P, Sondik EJ.eds.Cancercontrolobjectives for the nation: 1985-2000. Bethesda, Md: National CancerInstitute, 1986. US Dept of Health and Human Services publication NIH 8&-2880; No.2. 3. Guerry D. Control ofmortalityfrommalignantmelanoma. PigmentCell 1987;8:211-21. 4. Jensen OM.'Bolander AM.Trendsinmalignantmelanoma of the skin. World Health Stat Q 1980;33:2-26. 5. Roush cc, Schymura MJ, HolfordTR. Risk for cutaneous melanoma in recent connecticut birth cohorts. Am J Public Health 1985;75:679-82. 6. Horm JW, AsireAJ, YoungJL Jr, et ai, eds. SEER program: cancer incidence mortality in the United States, 1973-1981. Bethesda, Md: National Center for Health
Journal of the American Academy of Dermatology
Statistics, 1984. US Dept of Health and Human Services publication NIH 85-1837. 7. Mettlin C. Trends in years of potential life lost to cancer: 1970 to 1985. CA 1989;39:33-9. 8. Centers for Disease Control. Premature mortality in the United States:publichealth issuesin the use of yearsof potentiallife lost. MMWR 1986;35(supp12S):IS-11S. 9. Wise RP, Livengood JR, Berkelman RL, et al. Methodological alternatives for measuring premature mortality. Am J Prev Med 1988;4:268-273. 10. Arca M, DiOrioF, Forastiere F,etal. Yearsofpotentiallife loot (YPLL) before age 65 in Italy. Am J Public Health 1988;78:1202-5. 11. Christophersen ER. Automobile accidents: potential years of life lost. Pediatrics 1983;71:855-6. 12. Curran JW, Morgan WM, Hardy AM, et al. The epidemiology of AIDS: current status and future prospects.Science 1985;229:1352-7. 13. Haslett D. Smoking-related cancers and potential years of lifelost attributableto cigarette smoking, Ireland, 1968 to 1978.Ir J Med Sci 1984;153:309-9. 14. Krista! AR. The impact of the acquired immunodeficiency syndrome on patterns of premature death in New York City. lAMA 1986;255:2306-10. 15. Richter ED. Potential-years-life-loot from motor vehicle crashesin Israel:an epidemiologic analysis. Int J Epidemiol 1979;8:383-8. 16. Rockett IRH, Smith GS. Injuries in relation to chronicdisease: an international view of premature mortality. Am J Puhlic Health 1987;77:1345-6. 17. Dempsey M. Declinein tuberculosis: death rate failsto tell entire story. Am Rev Tuberc 1947;56:157-64. 18. WigleDT, Mao Y, Semenciw R, et al. Cancer patterns in Canada. Can Med Assoc J 1986;134:231-5. 19. Miller AB, ed.Screeningfor cancer. New York:Academic Press, 1985:10-1. 20. Social and economic implications of cancer in the United States. Washington,DC: US Dept of Health and Human Services, March 1981. US Dept of Health and Human Services publication PHS 81-1404,series 3, No. 20. 21. Devesa SS, Silverman DT, Young JL, et al. Cancer incidence and mortality trends among whites in the U.S., 1947-1984. JNCI 1987;79:701-70. 22. Centers for Disease Control. Premature mortality due to alcohol-related motor vehicle traffic fatalities-United States 1987. MMWR 1988;37:753-5. 23. Centersfor DiseaseControl.Years of potential life lost before age 65 due to perinatal conditions--United States, 1980-1983. MMWR 1987;36:179-87. 24. Romeder JM, McWhinnie JR. Potential years of life lost between I and 70: an indicator of premature mortality for health planning, Int J Epidemiol 1977;6:143-51. 25. Haenszel W. A standardization rate for mortality defined in unitsof lostyearsoflife.Am J Public Health 1950;40:1726. 26. Koh HK, LewRA, Prout MN. Screening for melanoma/ skin cancer: theoretic and practical considerations. J AM ACAD DERMATOL 1989;20:159-72.
Boston, Massachusetts Years of potential lifelost (YPLL) is an indicatorof premature mortalitythat complements traditional incidence and mortality rates and that facilitates comparisons among different cancers. We calculated YPLL from cutaneousmelanomaand 11 other cancersroutinelyrecorded and tracked by Surveillance, Epidemiology and End Results (SEER). YPLL from cutaneous melanoma ranked eighth for persons youngerthan 65 yearsof age and fourth for those 20 to 49 years of age. An averageof 17.1 YPLL per death were due to melanoma, one of the highest rates for adult-onset cancers.The resultsof our study, the first to apply YPLL to cutaneous melanoma, emphasize the disproportionate impact of this canceron youngand middle-aged adults and reemphasize the importance of this cancer as a public health priority. (J AM ACAD DERMATOL 1990;23:308-10.)
In 1990 cutaneous melanoma will strike 27,000 people, account for 5800 deaths,' and be responsible for the premature loss of numerous lives in the United States. The rate of increase in the incidence of cutaneous melanoma is projected to soon surpass that for virtually all other malignancies.e? As the incidence of cutaneous melanoma has risen, so has the mortality rate. Data from Surveillance, Epidemiology, and End Results (SEER)6 show that in 1981 the mortality rate for cutaneous melanoma was 2.0 per 100,000 population, up from 1.6 per 100,000 in 1973. SEER data also show that the mortality rate for melanoma ranks third among cancers in men and women 25 to 29 years of age and also ranks highly in the group 20 to 50 years of age. Overall mortality rates, however, do not reflect the ages at which persons die. Years of potential life lost (YFLL) is a simple measure that accounts for age at death together with the absolute number of deaths; it therefore indicates premature mortality.
From the Departments of Dermatology and Medicine, Boston University School of Medicine, and Section of Epidemiology and Biostatistics, Boston University School of Public Health. Sponsored in part by NCI grant IK07-CAOI38Q.Ol. Reprint requests: Howard K. Koh, MD, Boston University School of Medicine, 80 E. Concord St. C-321, Boston, MA 02118. "'Recipient of the Preventive Oncology Academic Award from the National Cancer Institute. 16jl/17Ci08
308
We applied this measure to cutaneous melanoma to demonstrate the disproportionately high impact of this cancer on young and middle-aged adults. METHODS
We used data obtained from Cancer Incidence and Mortality in the United States." SEER 1973 to 1981,to calculate YPLL beforeage 65 years for the 12 cancers that mostcommonly causedeath. Thesecancersand others are routinely recorded and tracked by SEER. The 1980 U.S. census population was used as the reference population.iThe numberof cause-specific deaths in each age intervalwas calculated by multiplying the mortality rate for each cancer by the sizeof the 1980U.S. population in each age interval. YPLL was defined as the summation of the number of cause-specific deaths occurring in 5-yearage intervals(beginning at birth) multiplied by the number of years remaining betweenthe midpoint of each 5-year age interval and the cutoff age of 65 years. YPLL per death was alsoderived for each cancer.
RESULTS YPLL and deaths for Americans up to 65 years of age resulting from the 12 cancers studied are shown in Table I. Cancers are presented in descending order of rank for YPLL per cancer death. Information on YPLL per death rank is followed by YPLL per death, YPLL rank, number of YPLL, and percentage of total YPLL; and rank, number, and percentage of deaths for each cancer. Mortality from cutaneous melanoma ranked elev-
Volume 23 Number 2, Part 1 August 1990
Years ofpotential life lost 309
Table I. Relative impact of 12 cancers in persons younger than 65 years in the United States (1980): YPLL rank, death rank, and YPLL per death Cancer site
RankoCYPLL per death
No.ofYFLL per death
1 2 3 4 5 6 7 8 9 10
2I.l 17.1 15.2 12.2 10.9 10.0 9.6 9.5 9.1 8.8 8.8 8.6
Adult leukemia" Melanoma"
Cervix" Breast Ovary Stomach Pharynx and larynx Colon Lung (non-small cell) Pancreas Esophagus Lung (small cell)
11
12
No. of deaths(%)
No.oC
YPLL(%)
6 8 9 2 7
10 11 3 1 5 13 4
55,882 48,131 43,730 217,625 53,745 43,372 34,706 117,356 333,258 60,229 31,810 66,377
(4.5) (3.9) (3.5) (I8) (4.4) (3.5) (2.8) (9.5) (27) (4.9) (2.6) (5.4)
12
11 10 2 6 7 8 3 1 5
9 4
2,649 2,816 2,885 17,799 4,922 4,349 3,633 12,386 36,701 6,815 3,605 7,704
(2.2) (2.4) (2.4) (15) (4.1) (3.7) (3.1) (10.4) (31) (5.7) (3.0) (6.5)
*YPLL rank is higher than death rank.
enth among the cancers and was responsible for 2.4% of the total number of cancer deaths. Cutaneousmelanoma accounted for 48,131 YPLL, or 3.9% of the total YPLL, and ranked eighth for YPLL of the 12 cancers. Cutaneous melanoma, however, was the second highestranking cancer on thelist in terms of YPLL per death, accounting for 17.1 YPLL per death (see Table I). The top five ranking cancers in terms of both mortality and YPLL in Table I head the list because of the sheer number of people who die from these cancers. Except for breast cancer, mortality from these cancers occurs largely after the fifth or sixth decade oflife, with YPLL per death lessthan 10. For the cancersranked sixththrough ninth bymortality, mortality was higher than YPLL in terms of percentage and ranking. However,melanomajoins two other cancers, adult leukemia and cervicalcancer, to rank higher in YPLL than in number of deaths, reflecting increased mortality earlier in adult life and at least 15 YPLL per death. DISCUSSION
YPLL, a measure of premature mortality, complementstraditionalmortality measuresby accounting for the age at whichdeath occurred. Becauseone of the primary goals of public health is to prevent premature mortality, the Centers for Disease Control has routinely calculated and tracked YPLL for the 15 major causesof death since 1979.7,8 In many ways such YPLL analyses reflectthe impact of disease in terms of human cost better than crude incidence and mortality data. They have been used for setting national priorities for cancer control, estab-
lishing guidelines in resource allocation, and monitoring the effectiveness of screening, treatment, and other health interventions"!" Although others18. 19 have applied YPLL to cancer in foreign countries, and YPLL measurements for cancer in the United States have been published in tabular form,2o our study is the firstto apply YPLL specifically to cutaneous melanoma. The results of our study emphasize the unfortunate impact of cutaneous melanoma on young and middle-aged adults. As with adult leukemia and cervical cancer, and in contrast to most other common cancers, mortality from melanoma tends to increase relatively early in adult life, resulting in disproportionately high premature cancer mortality and a relatively high toll in YPLL. For each death from melanoma,more than 17years of potential life before age 65 years are lost, second only to adult leukemia. Melanoma will undoubtedly advance in the ranking.The dramatic increase in incidence with the rise in mortality for cutaneous melanoma will increase YPLL; moreover, in contrast to many other cancers, age-specific increases in the incidence of cutaneous melanoma have been more pronounced in the middle-aged population compared with the older age groups.i' Monitoring this trend may be important for future planning and evaluation of health initiatives. 22 Most studies measuring YPLL, including those done by the Centers for Disease Control,8,23 use a cutoff age of 65 years for the calculations. Some researchers argue that age 70 or even 75 years would better represent the public health goal of postpone-
310 Albert et al. ment of death.24. 25 We agree with Wise et a1.,9 however, who studied YPLL in three different age rangesand recommended the cutoffage of 65 years. Wise et al. noted that 65 years is the traditional retirement age and is more effective in differentiating the leading causes of premature mortality from those affecting the entire population. Indicative ofthehighriskofmelanomainyounger persons is that, amongthe 12 cancerslisted inTable I, melanoma hasthe highestincidence in persons 20 to 24 yearsof age. 2 An excess of premature mortality argues for added efforts toward screening programs for the earlydetection of a particular cancer. Cutaneous melanoma is an appropriate cancer for screening because expensive testsand procedures for its early detection are not required and because an efficient, noninvasive examination of the skin followed by appropriate excision shouldpreventmetastatic disease and reduce mortality.26 In summary, our analysis shows that cutaneous melanoma makes a disproportionately high contributionto prematurecancermortalityand causes loss of many potentially productive years of life among young and middle-aged people. We believe melanoma should be further targeted as a publichealth priorityso that steps can be taken to prevent unnecessary death and suffering. Weare grateful to Cynthia Barber for her careful review of this manuscript, to Mary Beth Mercer for her assistance in this project, and to Dr. Claudia Arrigg for unending encouragement and support.
REFERENCES I. Cancer facts lind figures. New York: American Cancer Society, 1989. 2. Greenwald P, Sondik EJ.eds.Cancercontrolobjectives for the nation: 1985-2000. Bethesda, Md: National CancerInstitute, 1986. US Dept of Health and Human Services publication NIH 8&-2880; No.2. 3. Guerry D. Control ofmortalityfrommalignantmelanoma. PigmentCell 1987;8:211-21. 4. Jensen OM.'Bolander AM.Trendsinmalignantmelanoma of the skin. World Health Stat Q 1980;33:2-26. 5. Roush cc, Schymura MJ, HolfordTR. Risk for cutaneous melanoma in recent connecticut birth cohorts. Am J Public Health 1985;75:679-82. 6. Horm JW, AsireAJ, YoungJL Jr, et ai, eds. SEER program: cancer incidence mortality in the United States, 1973-1981. Bethesda, Md: National Center for Health
Journal of the American Academy of Dermatology
Statistics, 1984. US Dept of Health and Human Services publication NIH 85-1837. 7. Mettlin C. Trends in years of potential life lost to cancer: 1970 to 1985. CA 1989;39:33-9. 8. Centers for Disease Control. Premature mortality in the United States:publichealth issuesin the use of yearsof potentiallife lost. MMWR 1986;35(supp12S):IS-11S. 9. Wise RP, Livengood JR, Berkelman RL, et al. Methodological alternatives for measuring premature mortality. Am J Prev Med 1988;4:268-273. 10. Arca M, DiOrioF, Forastiere F,etal. Yearsofpotentiallife loot (YPLL) before age 65 in Italy. Am J Public Health 1988;78:1202-5. 11. Christophersen ER. Automobile accidents: potential years of life lost. Pediatrics 1983;71:855-6. 12. Curran JW, Morgan WM, Hardy AM, et al. The epidemiology of AIDS: current status and future prospects.Science 1985;229:1352-7. 13. Haslett D. Smoking-related cancers and potential years of lifelost attributableto cigarette smoking, Ireland, 1968 to 1978.Ir J Med Sci 1984;153:309-9. 14. Krista! AR. The impact of the acquired immunodeficiency syndrome on patterns of premature death in New York City. lAMA 1986;255:2306-10. 15. Richter ED. Potential-years-life-loot from motor vehicle crashesin Israel:an epidemiologic analysis. Int J Epidemiol 1979;8:383-8. 16. Rockett IRH, Smith GS. Injuries in relation to chronicdisease: an international view of premature mortality. Am J Puhlic Health 1987;77:1345-6. 17. Dempsey M. Declinein tuberculosis: death rate failsto tell entire story. Am Rev Tuberc 1947;56:157-64. 18. WigleDT, Mao Y, Semenciw R, et al. Cancer patterns in Canada. Can Med Assoc J 1986;134:231-5. 19. Miller AB, ed.Screeningfor cancer. New York:Academic Press, 1985:10-1. 20. Social and economic implications of cancer in the United States. Washington,DC: US Dept of Health and Human Services, March 1981. US Dept of Health and Human Services publication PHS 81-1404,series 3, No. 20. 21. Devesa SS, Silverman DT, Young JL, et al. Cancer incidence and mortality trends among whites in the U.S., 1947-1984. JNCI 1987;79:701-70. 22. Centers for Disease Control. Premature mortality due to alcohol-related motor vehicle traffic fatalities-United States 1987. MMWR 1988;37:753-5. 23. Centersfor DiseaseControl.Years of potential life lost before age 65 due to perinatal conditions--United States, 1980-1983. MMWR 1987;36:179-87. 24. Romeder JM, McWhinnie JR. Potential years of life lost between I and 70: an indicator of premature mortality for health planning, Int J Epidemiol 1977;6:143-51. 25. Haenszel W. A standardization rate for mortality defined in unitsof lostyearsoflife.Am J Public Health 1950;40:1726. 26. Koh HK, LewRA, Prout MN. Screening for melanoma/ skin cancer: theoretic and practical considerations. J AM ACAD DERMATOL 1989;20:159-72.