Skin cancer diagnosis and surgical management in general practice

Heal, Clare (2010) Skin cancer diagnosis and surgical management in general practice. PhD thesis, James Cook University.

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Abstract

Background

Skin cancer is an extremely important health issue in Australia. Squamous cell carcinoma (SCC) and basal cell carcinoma (BCC) are by far the commonest cancers in Australia with an incidence of more than four times that of all other registrable cancers combined.(1) Cutaneous melanoma (CM) is the fifth most common cancer in Australia, with the estimated risk of developing a melanoma before 75 years of age being one in 26 for Australian men and one in 36 for Australian women.(1) Queensland has the world's highest recorded incidence of all types of skin cancer,(2, 3) with incidence rates being even higher in tropical North Queensland.(4)

In North Queensland, the majority of suspicious skin lesions are managed by general practitioners (GPs),(5) particularly in rural centres such as Mackay where there is no resident plastic surgeon or dermatologist.(6) It is therefore important that the diagnosis and post surgical wound management of GPs is optimal.

In 2006 a group of GPs in Mackay, of which I was chief investigator, published a randomised controlled trial which showed that the wetting of sutures did not increase the incidence of wound infection but the incidence of infection was nevertheless higher than expected after minor skin cancer surgery.(7) This trial formed the background to several of the current studies for this thesis.

The overall aim of the studies presented here was:

1. To improve the management of skin cancer and the conduct of skin cancer surgery by Australian GPs.

2. To increase patient well-being through appropriate use of post-surgery wound management.

3. To assess the ability of GPs and pathologists to diagnose skin lesions.

4. To investigate possibilities of research in GP practice settings.

Methods

The thesis comprises the results of three trials which took part in the Queensland towns of Mackay and Townsville.

The first study proceeded from the 'Can sutures get wet' trial which was a randomised controlled trial conducted in general practice, in Mackay in 2004-5. Data were recorded from 1247 consecutive patients who attended for minor skin excisions. Further exploration and data analysis was undertaken from this trial to investigate 857 of these patients for risk factors for infection, to investigate the numbers needed to treat (by excision) for skin cancers and to examine the case-mix of skin lesions in regular general practice and a skin cancer clinic.

The second 'Topical chloramphenicol' study was also conducted in general practice in Mackay in 2007. This was a prospective double blinded randomised controlled trial. Nine hundred and seventy two patients were assessed for infection after receiving either a single topical dose of chloramphenicol (n=488) or paraffin ointment (n=484; placebo).

The third study had previously been conducted in Townsville and secondary data analysis from the database of this study formed the 'Diagnostic accuracy' and histological agreement studies. All excised and histologically confirmed skin cancers in Townsville/Thuringowa, from December 1996 to October 1999 were recorded. Positive predictive values (PPV) and sensitivities were calculated for the clinical diagnoses and stratified by histological sub-type and body-site. A stratified sample of 407 of 8,694 skin excisions slides was used to compare the "standard" histological diagnosis with the diagnosis from an internationally renowned dermato histo-pathologist.

Results

Secondary data analysis from the 'Can sutures get wet' study showed an overall incidence of infection was 8.6% (95%-confidence interval = [3.5, 13.8]). Excisions from lower legs and feet (p=0.009) or thighs (p=0.005), excisions of BCC (p=0.006) or SCC (p=0.002) and diabetes (p<0.001) were found to be independent risk factors for wound infection.

Close to half (46.7%) of lesions excised were skin cancers with more SCCs than BCCs (0.74:1). Our number needed to treat (NNT) (melanocytic naevi excised per melanoma) was 8.4. Mean age for excision of melanoma, BCC and SCC was 55, 60.9 and 63.8 yrs respectively. Relative tumour density was greatest in the face, scalp and neck region for all skin cancers.

Further analysis of these data comparing mainstream general practitioners with a doctor working in a designated skin cancer clinic showed that the case-mix of non-melanotic skin cancers was significantly different for the two groups of doctors (p<0.001). The BCC:SCC ratio was much higher for skin cancer clinic doctors (4:1) than for GPs (0.6:1). The NNT (melanocytic naevi excised per melanoma) was 4.7 for the skin cancer doctor and 9.0 for mainstream GPs.

In the 'Topical chloramphenicol' trial, the incidence of infection in the chloramphenicol group (6.6%; 95%-confidence interval = 95%-CI = (4.9 to 8.8)) was significantly lower compared to the incidence in the control group (11.0%; 95%-CI = (7.9 to 15.1)) (p=0.010). The absolute reduction in infection rate was 4.4%, the relative reduction was 40% and the relative risk of wound infection in the control group was 1.7 times higher (95%-CI = (1.1 to 2.5)) than in the intervention group.

The third and fourth studies examined a total of 8694 skin excisions reanalysed from the database of the Townsville study. Positive predictive values (PPV) for the clinical diagnoses were: BCC 0.727, SCC 0.494 and CM 0.333. Sensitivities for the clinical diagnosis were: BCC 0.639, SCC 0.411, and CM 0.338. For BCC, PPVs and sensitivities were higher for the trunk, the shoulders and the face and lower for the extremities. The reverse pattern was seen for SCCs.

Further analysis of the data comparing an expert dermato-pathologist with mainstream histo pathologists, showed positive predictive values for the primary histological diagnosis were above 90% for BCC, CM and CN. For SCC the positive predictive value was 72.6% (95%-CI = [65.5, 79.0]).

Overall conclusions

Patients with minor skin excisions in North Queensland have a higher incidence of wound infection. Groups at high risk of infection after minor surgery were diabetics, those undergoing excision of a non-melanocytic skin cancer or excision from the lower limb. Topical chloramphenicol ointment decreases this incidence moderately. GPs in North Queensland have a high yield of skin cancer from their skin excisions and a low NNT (melanocytic naevi excised per melanoma). Doctors diagnose skin cancers accurately, but there are some areas of diagnostic difficulty, in particular in the diagnosis of actinic keratosis (AK) and SCC. GPs and skin cancer doctors have a different skin cancer case-mix.

Overall recommendations

1. In view of the level of skin infection associated with skin cancer surgery previously identified, antibiotic prophylaxis prior to minor surgery in general practice should be limited to the high risk groups that were identified - the consequences of infection are often minor and side-effects from antibiotics, such as allergy, can potentially be serious.

2. The use of topical chloramphenicol ointment to prevent infection after minor surgery is best reserved for high risk groups. The reduction in infection was only 40%, which was statistically but not clinically relevant. The overutilization of topical antibiotics has potentially adverse consequences such as antibiotic resistance and allergic contact dermatitis.

3. The doctors involved in my study in Mackay could consider lowering their threshold for excision of pigmented lesions. In our sample of Mackay GPs, there was a very high yield of skin cancers from all excisions, and NNT (melanocytic naevi excised per melanoma) of 8.4, was lower than published data from comparable cohorts.

4. Educational programs for doctors regarding the diagnosis of skin cancer could focus on areas of diagnostic weakness which were identified in our study, such as differentiating melanocytic naevi from malignant melanoma, and differentiating between AK and SCC.

5. It is important that doctors excising suspicious skin lesions are aware that there is discordance and lack of agreement between histopathologists regarding the diagnosis of SCC and AK.

Item ID: 19038
Item Type: Thesis (PhD)
Keywords: carcinomas; chloramphenicol; diagnosis; general practitioners; GPs; management; melanomas; minor excisions; skin cancer clinics; skin cancer; surgery; sutures; wound healing; wound infection
Related URLs:
Additional Information:

Publications arising from this thesis are available from the Related URLs field. The publications are:

Appendix 1: Heal, Clare, Buettner, Petra, and Browning, Sheldon (2006) Risk factors for wound infection after minor surgery in general practice. Medical Journal of Australia, 185 (5). pp. 255-258.

Appendix 2: Heal, Clare F., Buettner, Petra G., Cruickshank, Robert, Graham, David, Browning, Sheldon, Pendergast, Jayne, Drobetz, Herwig, Gluer, Robert, and Lisec, Carl (2009) Does single application of topical chloramphenicol to high risk sutured wounds reduce incidence of wound infection after minor surgery? Prospective randomised placebo controlled double blind trial. British Medical Journal, 338 (7688)

Appendix 3: Heal, Clare, Buettner, Petra, Raasch, Beverley, and Browning, Sheldon (2006) Minor skin excisions in general practice in North Queensland. Australian Family Physician, 35 (10). pp. 825-828.

Appendix 4: Heal, Clare F., Raasch, Beverley A., Buttner, Petra, and Weedon, David (2008) Accuracy of clinical diagnosis of skin lesions. British Journal of Dermatology, 159 (3). pp. 661-668.

Appendix 5: Heal, Clare, Weedon, David, Raasch, Beverley, Hill, Brendon, and Buettner, Petra G. (2009) Agreement between histological diagnosis of skin lesions by histopathologists and a dermato-histopathologist. International Journal of Dermatology, 48 (12). pp. 1366-1369.

Appendix 6: Heal, Clare, and Raasch, Beverley (2008) Diagnosing skin cancer in primary care: how do main-stream general practitioners compare with primary care skin cancer clinic doctors? Medical Journal of Australia, 188 (2). p. 125.

Appendix 7: Heal, Clare F., Veitch, Craig, and Preston, Robyn (2008) Practice based research: lessons from the field. Australian Family Physician, 37 (4). pp. 381-384.

Appendix 19: Heal, Clare, Buttner, Petra, Raasch, Beverley, Browning, Sheldon, Graham, David, Bidgood, Rachel, Campbell, Margaret, and Cruikshank, Robert (2006) Can sutures get wet? Prospective randomised controlled trial of wound management in general practice. British Medical Journal, 332 (7549). pp. 1053-1056.

Date Deposited: 15 Apr 2015 02:29
FoR Codes: 11 MEDICAL AND HEALTH SCIENCES > 1112 Oncology and Carcinogenesis > 111204 Cancer Therapy (excl Chemotherapy and Radiation Therapy) @ 34%
11 MEDICAL AND HEALTH SCIENCES > 1112 Oncology and Carcinogenesis > 111202 Cancer Diagnosis @ 33%
11 MEDICAL AND HEALTH SCIENCES > 1103 Clinical Sciences > 110323 Surgery @ 33%
SEO Codes: 92 HEALTH > 9201 Clinical Health (Organs, Diseases and Abnormal Conditions) > 920102 Cancer and Related Disorders @ 34%
92 HEALTH > 9201 Clinical Health (Organs, Diseases and Abnormal Conditions) > 920117 Skin and Related Disorders @ 33%
92 HEALTH > 9202 Health and Support Services > 920299 Health and Support Services not elsewhere classified @ 33%
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