Probability of malignancy in SPN in patients with previous malignancy  
A frequent problem is a SPN in a patient with a history of a previous malignancy. As with any nodule, treatment depends on whether the nodule is benign or malignant. In patients with prior malignancy, intuitively the odds that the lesion is a metastasis increases. Whether the nodule is a metastasis or a new primary is also important in treatment  

Determining Risk of Malignancy: Likelihood ratios

Derived from a 5 year retrospective review of 149 patients with extrapulmonary malignancies. SPN (minimum size 5.0 mm) could be either synchronous or metachronous. The likelihood that a patient with a SPN has a malignancy (either primary or metastatic) is 4.26:1 similar to the 4.95:1 ratio derived from the data of Cahan.
(from Quint et al).

  Likelihood of malignancy in patient with SPN:
 

 
Extrapulmonary malignancy
# of patients
% with metastasis
% with lung cancer
% with benign
Head & Neck squamous cell
33
9
76
15
Lymphoma or leukemia
14
0
57
43
Carcinoma: urinary bladder, breast, cervix, bile ducts, esophagus, ovary, prostate, stomach
45
18
58
24
Carcinoma: salivary gland, adrenal, colon, parotid, kidney, thyroid, thymus, uterus
31
52
42
6
Melanoma, sarcoma, testis
38
60
24
16
Likelihood Ratios:

Likelihood ratios are intuitive measures of the diagnostic information provided by a test result or clinical finding. The likelihood ratio varies from zero to infinity, depending on the degree of strength of the test result. A test strongly suggestive of aortic rupture has a likelihood ratio much greater than one, a test that suggests no rupture has a likelihood ratio close to zero, and a test that contains no diagnostic information has a likelihood ratio of one. In the odds-likelihood ratio form of Bayes theorem, the odds that the aorta is ruptured is the product of the likelihood ratios favoring aortic rupture multiplied by the prior odds of aortic rupture.

Equations:

Bayes Theorem:
Posterior odds = prior odds x likelihood ratios

Likelihood Ratios:

= Prob in subjects with aortic rupture / Prob in subjects without aortic rupture
= Sensitivity / (1 - Specificity)
= True positive fraction / False positive fraction

Probability:

Probability = Odds / (Odds + 1)
Odds = Prob / (1 - Prob)
References

Cahan WG, Shah JP , Castro EB. Benign solitary lung lesions in patients with cancer. Ann Surg 1978; 187:241-244.

Quint LE, Park CH , Iannettoni MD. Solitary pulmonary nodules in patients with extrapulmonary neoplasms. Radiology 2000; 217:257-261.

Disclaimer:

Information provided is not intended to be medical or technical advice. The information given at this site is for educational purposes only and is not sufficient for medical decisions. I disclaim any liability for the acts of any physicians or any other individual who receives any information on any medical procedure through this web site. I accept no legal responsibility for any injury and/or damage to persons or property from any of the suggestions or material discussed herein.