Data Exploration
Clinical Data
First, download the clinical data. Here we are using the TCGA skin cutaneous melanoma (SKCM) cohort.
clin_df <- SuMu::get_tcga_clinical(cohort = "SKCM")
## format some clinical data variables
clin_df2 <- clin_df %>%
dplyr::mutate(stage_part1 = gsub(pathologic_stage,
pattern = '(Stage [0I]+).*',
replacement = '\\1'),
diagnosis_year_group = cut(year_of_initial_pathologic_diagnosis,
breaks = c(1975, 1990, 1995, 2000,
2005, 2010, 2015, 2020),
include.lowest = TRUE),
os_10y = ifelse(OS_IND == 1 & OS <= 10*365.25, 1, 0),
sample = sampleID
)Review clinical data
For this analysis we will consider the survival time in since initial pathologic diagnosis.
fit <- survfit(Surv(OS, OS_IND) ~ 1,
data = clin_df2)
survminer::ggsurvplot(fit) +
ggtitle('Survival since diagnosis in full cohort')
Plotting by stage, although the time of ‘stage’ determination may be confounded if not collected at time of initial diagnosis.
fit <- survfit(Surv(OS, OS_IND) ~ pathologic_stage,
data = clin_df2)
survminer::ggsurvplot(fit, legend = "right")
There also seem to be differences by tumor type.
fit <- survfit(Surv(OS, OS_IND) ~ sample_type,
data = clin_df2)
survminer::ggsurvplot(fit, legend = "right")
(Aside: I wonder how similar tumor type is to sample type? For example, we could have a metastatic patient where the sample was obtained from the primary tumor. We will want to adjust our genetic data analysis for the sample type but may want to estimate prognosis according to the tumor type?)
A variable like year_of_initial_pathologic_diagnosis is guaranteed to be unconfounded since we can safely assume it was collected at the time of diagnosis.
fit <- survfit(Surv(OS, OS_IND) ~ diagnosis_year_group,
data = clin_df2)
survminer::ggsurvplot(fit, legend = 'right')
This makes it pretty clear that we have a strong “survival” bias to our data. This would suggest that, among people whose diagnosis was made in the 90s, only those who survived long enough to be enrolled were included in the study.
Let’s look at a histogram of years of initial diagnosis.
ggplot(clin_df2, aes(x = year_of_initial_pathologic_diagnosis,
fill = diagnosis_year_group)) +
geom_histogram() +
theme_minimal()
Let’s look at the time since initial diagnosis (presumably, the time from enrollment to diagnosis).
Finally, we can visualize a more comprehesive set of clinical variables.
fit <- survival::coxph(Surv(OS, OS_IND) ~
age_at_initial_pathologic_diagnosis +
sample_type +
breslow_depth_value + initial_weight +
strata(year_of_initial_pathologic_diagnosis),
data = clin_df2)
print(fit)## Call:
## survival::coxph(formula = Surv(OS, OS_IND) ~ age_at_initial_pathologic_diagnosis +
## sample_type + breslow_depth_value + initial_weight + strata(year_of_initial_pathologic_diagnosis),
## data = clin_df2)
##
## coef exp(coef) se(coef) z
## age_at_initial_pathologic_diagnosis 0.018324 1.018493 0.006078 3.01
## sample_typeMetastatic 0.697124 2.007970 1.046439 0.67
## sample_typePrimary Tumor 1.156752 3.179590 1.077900 1.07
## breslow_depth_value 0.014482 1.014587 0.008354 1.73
## initial_weight -0.000223 0.999777 0.000471 -0.47
## p
## age_at_initial_pathologic_diagnosis 0.0026
## sample_typeMetastatic 0.5053
## sample_typePrimary Tumor 0.2832
## breslow_depth_value 0.0830
## initial_weight 0.6362
##
## Likelihood ratio test=16.3 on 5 df, p=0.00607
## n= 338, number of events= 166
## (143 observations deleted due to missingness)Somatic Mutations Data
We can download the somatic mutations to supplement the phenotypes.
mut_df <- SuMu::get_tcga_somatic_mutations(cohort = "SKCM") %>%
dplyr::mutate(gene_aa = paste0(gene, ".", Amino_Acid_Change),
gene_effect = paste0(gene, ".", effect)
)Check the most frequent mutations.
mut_df_missense = mut_df %>% dplyr::filter(effect == "Missense_Mutation")
mut_df_missense$gene_aa = paste0(mut_df_missense$gene, ":", mut_df_missense$Amino_Acid_Change)
mut_df_missense %>% select(gene_aa) %>% table %>% sort %>% rev %>% as.data.frame %>% head(10)## . Freq
## 1 BRAF:p.V600E 206
## 2 NRAS:p.Q61R 56
## 3 BRAF:p.V600M 40
## 4 NRAS:p.Q61K 38
## 5 NRAS:p.Q61L 19
## 6 RAC1:p.P29S 17
## 7 IDH1:p.R132C 15
## 8 SPTLC3:p.R97K 13
## 9 SLC27A5:p.T554I 13
## 10 MAP2K1:p.P124S 13Filter to top genes
top_genes <- mut_df %>%
dplyr::group_by(gene) %>%
dplyr::mutate(gene_count = n()) %>%
dplyr::ungroup() %>%
dplyr::distinct(gene, .keep_all = TRUE) %>%
dplyr::top_n(gene_count, n = 10) %>%
dplyr::select(gene)
mut_df_topgenes <- mut_df %>%
dplyr::semi_join(top_genes)